Preheat oven to 350 degrees Fahrenheit 20 minutes before baking your cupcakes. Spray a miniature muffin pan with nonstick spray and set aside.
Onto a parchment paper, sift together cake flour, baking powder, baking soda, and salt; set aside. In a mixing bowl, beat the butter and sugar until light and fluffy, 2-3 minutes, scraping down the sides of the bowl as needed. Add the egg yolks 1 at a time, beating well after each addition. Once all of the egg yolks are incorporated, add the vanilla extract and mix in.
Alternately add the dry ingredients and the buttermilk, ⅓ at a time, mixing well after each addition. Start with ⅓ of the dry, mix well, and then add ⅓ of the buttermilk, and repeat two more times with remaining ingredients. Once everything is incorporated, beat well with a rubber spatula to make sure your batter is fully mixed and fluffy.
Scoop batter into prepared muffin pan. Bake for 18-22 minutes, rotating the pan halfway through the baking time. When cupcakes are done, the tops should be golden brown and spring back when lightly pressed in the center. A cake tester should come out clean. Remove the pan to a cooling rack. Let rest 5 minutes. Run a small knife or metal spatula around the sides of the cupcakes and invert onto a cooling rack. Let cupcakes cool to room temperature.
In a standing mixer fitted with a whisk, mix together sugar and butter. Mix on low speed until well blended and then increase speed to medium and beat for another 3 minutes. Add vanilla and cream and continue to beat on medium speed for 1 minute more, adding more cream if needed for spreading consistency. Pipe frosting onto cooled cupcakes and decorate with your choice of sprinkles!