Preheat oven to 350°F and line a muffin tin with 12 liners. Line a second muffin tin with 3 more liners - this recipe makes 15 cupcakes.
In a medium bowl, combine 1 ¾ flour, baking powder, and salt and set it aside.
In the bowl of a standing or handheld mixer, beat together the butter and sugar until light and fluffy, around 1-2 minutes. Add in the eggs and egg white, one at a time, then add in the vanilla extract and milk.
Pour in the dry ingredients and mix until just combined. Do not over-mix!
Put 1 tbsp of flour in a seperate bowl and toss the frozen raspberries in it until they are covered in flour. If the raspberries are really big you can break them up a little bit, but not too small.
Fill the muffin tins ½ way with cupcake batter then push 3-5 raspberries into each one. This will create perfectly white cupcakes with bright pops of raspberry. You can also fold the raspberries right into the batter before filling the muffin liners, but this will create streaks of color throughout the cupcakes.
Bake the cupcakes for 16-22 minutes or until a toothpick inserted in the middle comes out clean. Let cool completely while you make the Raspberry Buttercream.