Whisk together the cake flour, milk powder, cornstarch, baking powder, and salt in a medium bowl and set aside.
With a hand mixer or stand mixer fitted with the paddle attachment, beat together the softened butter and vegetable shortening in a large bowl until homogeneous.
Add in the powdered sugar and granulated sugar and mix until light and fluffy, about 3-4 minutes.
Mix in the egg, egg white, vanilla extract, almond extract, and heavy cream until incorporated.
Using a rubber spatula, fold in all of the dry ingredients until a smooth dough forms with no more streaks of flour. Cover the bowl with plastic wrap and chill in the fridge for at least 1 hour.
In the meantime, preheat the oven to 325℉ and line a baking sheet with parchment paper.
When ready to bake, remove the bowl from the fridge and use a 2-tablespoon scoop to portion out the cookies.
Roll each ball of dough into a smooth sphere. If the dough sticks to your hands, lightly dampen your palms with water and continue rolling.
Evenly space the dough onto the baking sheet with a 2'' gap in between each cookie.
Bake for 12-15 minutes or until the cookies are barely golden brown on the edges and set in the middle. Do not overbake.
Let the cookies cool to room temperature before assembling. In the meantime, prepare the frosting.
To make the buttercream, beat together the softened butter and vegetable shortening with a hand mixer or stand mixer fitted with the paddle attachment. Once homogeneous, gradually add in the powdered sugar and mix until smooth.
Stir in the vanilla extract, almond extract, heavy cream, and any food coloring of choice. If the buttercream is too thick, add milk or heavy cream one tablespoon at a time until the correct consistency is reached.
When ready to assemble, use an offset spatula or piping bag to spread a layer of frosting over each cookie. Smooth the top of the frosting and garnish with sprinkles before serving.
Enjoy cookies immediately or let the frosting fully set before storing in an airtight container for up to 3 days.