Preheat the oven to 350°F. Line a 12-cup muffin tin with cupcake liners.
In a stand mixer fitted with a paddle attachment, stir together the flour, sugar, baking powder, and salt.
Turn the mixer to low and beat in the butter for 1 minute. Turn speed to medium and beat 30 seconds, or until the butter is combined and the mixture is coarse in texture.
Reduce the speed to low, and mix in the buttermilk, vanilla extract, and vanilla bean paste for 1 minute, or until combined. Turn the mixer to medium and beat 30 seconds. Scrape the sides of the bowl.
Turn the mixer to low, and add egg. Pour in the egg white and mix on medium-high for 30 seconds, or until the batter is smooth. Fold in M&M's. Pour the batter evenly into the cupcake liners, about 3/4 full.
Bake 18 to 22 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let cool 5 minutes in the pan before transferring cupcakes to a rack to cool completely.
Frost cooled cupcakes using a 1M or 1A frosting tip. Top each cupcake with a few M&M's.
Notes
Make Ahead: Measure out all of the dry ingredients and keep them stored in a sealed jar as a great gift or to make a quick cake or cupcakes when the mood strikes. From Cake Mix: Follow this easy vanilla cupcake recipe to start with a cake mix. Then follow with adding the M&M's and frosting after they've been baked and cooled.Vanilla: Use a really good vanilla extract or vanilla bean paste, since these cupcakes rely heavily on its flavor. Frosting: Two of my favorites are classic buttercream frosting and chocolate buttercream frosting.