Prepare the pans. Heat the oven to 350°F (175°C). Grease both pans, line the bottoms with parchment, then grease the paper.
Whisk the flour, baking powder, and salt. Keep this mixture beside the mixer so it can be added in stages.
Beat cake butter and granulated sugar for 3–4 minutes until fluffy. Scrape the bowl, then beat in eggs individually and add vanilla.
Mix in the flour in three additions, alternating with milk in two additions. Use low speed and stop when the flour disappears.
Divide the batter evenly between pans. Bake 28–33 minutes, until the centers spring back and a tester shows no wet batter.
Cool in the pans for 10 minutes. Turn out onto a rack, peel away parchment, and cool completely before assembling.
Beat frosting butter until smooth. Gradually add powdered sugar, vanilla, salt, and 3 tablespoons cream; whip 2 minutes, adding remaining cream only if needed.
Sandwich the layers with buttercream, then cover the top and sides. Finish with sprinkles and cut with a clean sharp knife.
