Preheat the oven to 350°F (175°C). Grease and flour two 8-inch cake pans, then line the bottoms with parchment for easy release.

Whisk together the flour, baking powder, and salt until evenly combined. Set aside.

Beat the butter and sugar on medium-high speed for about 3 minutes until pale and fluffy. The texture should feel light and airy.

Reduce speed and add eggs one at a time, mixing well after each addition. Stir in vanilla extract. If the mixture looks slightly curdled, keep mixing until smooth.

Add the flour mixture in three parts, alternating with the milk in two parts, beginning and ending with flour. Mix just until combined to keep the cake tender.

Divide the batter evenly between pans and smooth the tops. Bake for 30–35 minutes, until a toothpick inserted comes out mostly clean and the tops spring back lightly.

Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Whisk egg whites and sugar in a heatproof bowl. Place over simmering water and whisk constantly until it reaches 160°F or feels smooth with no graininess.

Transfer to a mixer and whip on medium-high speed until stiff peaks form and the bowl feels cool.

Switch to a paddle attachment and slowly add butter cubes, mixing until smooth. Add vanilla and beat until creamy. If it looks curdled, continue mixing until it comes together.

Place one cake layer on a stand, spread about 1 cup of frosting, then add the second layer. Apply a thin crumb coat and chill for 20 minutes.

Finish frosting the cake smoothly, then decorate with sprinkles and pipe rosettes if desired.