Make the buttercream: With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy, about minuteAdd the confectioners' sugar, heavy cream, and vanilla extractBeat on low speed for 30 seconds, then increase to mediumhigh speed and beat for 2 full minutesAdd up to 1/4 cup (30g) more confectioners' sugar if frosting is too thin or a splash of heavy cream if frosting is too thickAdd a pinch of salt if frosting is too sweet(I add a small pinch.)

Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the butter on high speed until smooth and creamy, about minuteAdd the sugar and beat on high speed until creamed together, about 1 minuteScrape down the sides and up the bottom of the bowl with a rubber spatula as neededOn high speed, beat in the egg whites until combined, then beat in the sour cream and vanilla extractScrape down the sides and up the bottom of the bowl as neededPour the dry ingredients into the wet ingredientsTurn the mixer to low speed and as the mixer runs, slowly pour in the milkBeat on low speed just until all of the ingredients are combinedDo not overmixYou may need to whisk it all by hand to make sure there are no lumps at the bottom of the bowlThe batter will be slightly thickGently fold in the sprinkles.

teaspoon pure vanilla extract

Make Ahead & Freezing Instructions: Prepare cake through step Wrap the baked and cooled cake tightly and keep at room temperature for 1 day or freeze up to 3 monthsBring to room temperature (if frozen) then continue with step 7Frosting can also be made 1 day ahead of timeCover tightly and refrigerate overnightBring frosting to room temperature, then beat the frosting on medium speed for a few seconds so it's creamy againAdding a splash of cream/milk will help thin the frosting out, if neededFrosted cake freezes well, up to 3 monthsThaw overnight in the refrigerator, then bring to room temperature or serve coldSee How to Freeze Cakes .

Preheat oven to °F (177°C)Grease a 9×2 inch round cake pan, line with a parchment paper round (see #6 in Cake Baking Tips ), then grease the parchment paperParchment paper helps the cake seamlessly release from the panI recommend using nonstick spray for greasing.

Bake for around minutes or until the cake is baked throughAfter about 18 minutes, tent the cake with aluminum foil to prevent the top and edges from overbrowningTo test the cake for doneness, insert a toothpick into the center of the cakeIf it comes out clean, it's done.

salt , to taste

optional: sprinkles for garnish

Instructions

Make the cake: Whisk the cake flour, baking powder, baking soda, and salt togetherSet aside.

Pour batter evenly into prepared cake pan.

Allow cake to cool completely in the pan set on a wire rackThe cake must be completely cool before frosting.

Spread frosting all over the topI always use an icing spatula Top with sprinkles, if desired.

Notes