Oatmeal Cream Pies With Marshmallow Buttercream Filling

Step away from the store-bought, prepackaged oatmeal cream pies and try your hand at making them homemade instead! Trust me, it’s a lot easier than you might think and the results are out-of-this-world (ask my kids if you don’t believe me)!

I get it, oatmeal cream pies are one of the most iconic store-bought sweet treats that we all grew up enjoying. However, have you noticed that over the years the price keeps going up while the contents inside the wrapper keep getting smaller and smaller?

And don’t get me started on all of those ingredients! I stopped counting when I got to 30 (however, not before I saw that the cookies included the dreaded “Red 40 Lake”). These sandwich cookies you can make right in your own kitchen using ingredients that you likely already have on hand in your pantry and fridge. No food coloring needed!

The result is soft and chewy oatmeal cookies sandwiched around a marshmallow buttercream filling that are way better than the store-bought sandwich cookies anyway! The oatmeal cookies alone are delicious without the addition of the homemade buttercream, but that filling takes them way over the top!

These oatmeal cream pies are not for the faint of heart, however! They are a decadent sweet treat that will have you never wanting to grab the prepackaged kind again!

How To Make Homemade Oatmeal Cream Pies With Marshmallow Buttercream Frosting

*Scroll down to the bottom of this post to see the full recipe, including exact measurements and amounts. You can also print out the instructions. I go into a bit more detail about the recipe here first, just in case you need it.

Ingredients

I’ve broken down the ingredients into the cookies and the filling. Together, they make around 16 sandwich cookies, give or take depending on how big you scoop out the cooking dough.

Oatmeal Cookie Ingredients

• Salted Butter – I always have salted stick butter on hand so that is what the recipe is based on. If you use unsalted butter, just increase the amount of salt in the recipe slightly. Either way, the butter needs to be softened.
• Granulated sugar – Any kind works just fine.
• Light Brown Sugar – When measuring the brown sugar for this recipe, ensure that you are packing it down well. The sugar should hold the shape of your measuring cup when you dump it out if you pack it firmly enough.
• Vanilla Extract – We use our homemade vanilla extract but you can use any kind of pure vanilla. Just avoid using imitation. The flavor just doesn’t compare.
• Eggs – The eggs should be at room temperature before use.
• Flour – Any kind of all-purpose flour will work, but we like to use unbleached flour.
• Baking Soda – This is the rising agent that helps the cookies puff up a bit while baking.
• Cinnamon – Even though this might seem like an odd seasoning to add, the cinnamon flavor is mild and not overpowering in the oatmeal cookies. It just adds a slight bit of warmth.
• Salt – This recipe only calls for 1/4 teaspoon of salt if you are using salted butter. If using unsalted, increase it to 1/2 teaspoon salt.
• Quick Oats – I have only made this recipe using quick oats. You can definitely try using old fashioned instead, but the results might not be as good. The quick oats produce a cookie that is soft and chewy with slightly crispy edges.

Marshmallow Buttercream Filling Ingredients

• Powdered Sugar – Don’t use granulated sugar here because we want a nice and smooth buttercream filling.
• Butter – Again, I use salted stick butter. If you use unsalted, add a pinch of salt to your buttercream filling when making.
• Marshmallow Fluff – This is the special ingredient that helps to take this oatmeal cream pie filling over the top! The result is a cream that is light and fluffy but with a hint of decadent marshmallow flavor. You can make your own homemade if you would prefer but I’ve never tried it in this recipe.
• Vanilla Extract – Again, don’t reach for the imitation stuff. Use the real deal here!
• Half and Half – This is to help thin out the filling slightly. Start with using the lower end of the measurement and add more after mixing if the filling appears too thick. Just don’t add too much because you don’t want to end up with a runny filling. It needs to have enough body to hold its shape after you pipe it onto the cookies. You can also use whole milk, 2% milk, or even heavy whipping cream as an alternative.

Instructions For Oatmeal Cream Pies

First, we are going to start by making and baking the oatmeal cookies. These cookies are honestly delicious on their own, so feel free to save the recipe just for the cookies!

Begin by preheating your oven to 350º Fahrenheit. Grab a cookie sheet or two and line them with parchment paper. We like to use unbleached parchment paper that we can compost, but feel free to use whatever you have on hand. Set those aside for now. (Product Link: Reynolds Kitchens Unbleached Parchment Paper)

Now, I like to use a stand mixer to make these oatmeal cream pies. However, you can definitely mix them by hand. It will just take a bit more time and muscles (which I am lacking currently).

Mixing The Wet Ingredients

In your stand mixer with a paddle attachment (or a large bowl), cream together the softened butter, granulated sugar, and packed brown sugar. Continue mixing until it is nice and fluffy. The color should be off-white when you’ve mixed long enough.

Next, add the vanilla and the room-temperature eggs. Mix well, scraping the sides of the bowl if needed with a spatula. Set aside.

Mixing The Dry Ingredients And Baking

In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt. If you are using unsalted butter, increase the amount of salt slightly. You need the salt in there to help balance out the sweetness of everything else.

Add your dry ingredients to the wet ingredients and mix until just combined. You don’t want to overmix here. Remove the bowl from the stand mixer and gently fold in the oats using a spatula or spoon.

Now’s the time to grab those prepared cookie sheets. Using a 1.5 tablespoon cookie scoop, drop little dough balls onto the parchment paper. You should be able to get about 12 cookies per sheet (3 rows of 4). You don’t want the dough too close because the cookies will expand some while baking. (Product Link: Prep Solutions by Progressive 1.5 Tbsp Measuring Scoop)

Bake the cookies for 10 to 12 minutes or until the edges of the cookies start to turn golden brown. For my oven, this was right at 12 minutes.

Remove the baking sheet from the oven and allow the cookies to cool for a few minutes before transferring to a cooling rack. If you try to remove them too soon, the cookies will likely crumble apart.

Let the cookies cool fully before adding the marshmallow buttercream filling. Otherwise, you will have a melted mess of filling on your hands – literally!

Making The Marshmallow Buttercream Filling

Clean stand mixing bowl so you can use it now for the filling. Again, you can make this without a stand mixer, but it is a lot easier using the stand mixer or even a handheld mixer.

Using the paddle attachment again, add all of the filling ingredients together into the bowl. Start by using the lower amount of half and half. Mix the ingredients well. You will likely need to use a spatula to scrape the sides of the bowl occasionally to make sure everything gets well incorporated.

Continue to mix the filling on low for 1 to 2 minutes until it becomes light and fluffy. If the cream appears too thick, add an additional tablespoon of half and half after mixing. Just keep in mind that you don’t want the filling to be too runny. It needs to be able to hold its shape once you pipe it onto the cookies.

Filling The Oatmeal Cream Pies

Add the cream filling to a pastry bag with a wide circular tip. If you don’t have a pastry bag, you can just use a heavy ziplock bag with one of the corners snipped off. (I use the 2A round tip from this set – Product Link: Wilton Cupcake Decorating Set Piping Bags And Tips Set.)

Going in a circular motion, pipe the marshmallow buttercream filling to the bottom of one of the cookies. Leave a little space around the edge of the cookie so the filling can expand slightly when you sandwich the two cookies together.

Next, add a similar-sized cookie to the top so that the bottom of each cookie is touching the filling. Gently press them together until the filling expands out to the edge.

Place the finished oatmeal cream pies in the refrigerator to help set the filling. After setting, you can either allow them to come to room temperature before eating or you can enjoy them right from the fridge! Store any leftovers in an airtight container in your refrigerator. Enjoy!

For other sweet desserts, check out some of my other recipes:

• Soft & Chewy Scotcheroos
• Fudgy Chocolate Chip Brownies
• Shortcut Carrot Bars With Cream Cheese Frosting
• Sourdough Discard Chocolate Chip Cookies
• Homemade Chocolate Fudge

Until next time, thanks for stopping by!
– Chelsea

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