Preheat oven to 350 degrees.
Set up your cupcake pan with liners.
Whisk the flour, baking powder, salt, and baking soda together in a medium bowl.
In a separate large mixing bowl, beat butter with an electric mixer or Kitchenaid on medium to high for 30 seconds.
Add sugar, vanilla, and almond extract to the butter and beat until combined.
Add egg whites and eggs one at a time, beating well after each.
Add the flour mixture and buttermilk, alternating between the two, to butter mixture, beating on low speed until everything is well mixed together
Fill the cupcake pan liners 2/3 with cake batter
Bake for 18-20 minutes.
Remove cupcakes from pan and allow to cool on a wire rack for 30 minutes before frosting
Using an electric mixer, combine all ingredients at medium speed and work your way up to high.
If icing too stiff, add milk one tablespoon at a time. If too watery, add icing sugar 1 tablespoon at a time.
Add blue food coloring a couple of drops at a time to your buttercream icing until you reach your desired color.
Using an offset spatula, spread blue icing generously on cupcake top
Top with marshmallow pieces cut into quarters, so they look like glaciers coming out of the water. You can also use mini marshmallows to create the effect.
Sprinkle with crystal blue sprinkles.