In a large bowl, mix together flour, baking powder, salt, and sugar. Set aside.
In a smaller bowl, combine melted butter, egg, milk, and vanilla. Mix thoroughly. Add the liquid ingredients to the dry, mixing only until just combined. It's ok if there are still clumps in the batter. Set aside.
Combine the topping ingredients in a small bowl. Once well mixed, add about 2/3 of the topping into the batter bowl. Slowly fold in the topping until there are ribbons of it going throughout. It should not be completely mixed in!
Add tall cupcake liners to a muffin tin. Scoop 3 Tbsp of batter into each muffin liner. Evenly sprinkle the rest of the topping onto the tops of each muffin. **Please see the note below if you are not using tall muffin liners.
Bake the muffins for 12 to 15 minutes until a toothpick comes out clean.
While the muffins are baking, make your frosting glaze. Add powdered sugar, milk, and vanilla to a small bowl and combine until smooth. Add a bit more milk if the glaze seems a bit too thick for your liking.
Once the time is up, remove the muffins from the oven. The tops may look gooey from the melted topping. Allow the cinnamon roll muffins to cool slightly before adding your glaze. Enjoy!
Notes
**This recipe works best when using tall muffin liners. If not, the batter will likely expand and overflow the tops of the cups. This is fine, but just something to keep in mind when baking. You can fill up each cup with 2 Tbsp of batter if you wish to prevent this. If going this route, you should have enough batter left over to make a few more muffins in a second batch. If still using the full 3 Tbsp, I highly suggest placing a baking sheet in the bottom of your oven to catch any overflow. Just be sure to grease your muffin tin well. I've made them plenty of times without the tall liners. While they might look messy, they are still super yummy!