Yellow butter layer cake with chocolate cream cheese frosting

Butter the cake pans, lay in a parchment round and butter again.

Whisk the cake flour, baking powder, kosher salt and baking soda together.

Cream the butter, the oil and the sugar on low, then higher, for several minutes until pale, airy and whipped-looking.

On medium, add the eggs and yolks one at a time so each emulsifies, speeding the mixer up after each addition and scraping the bowl down well.

Add the vanilla extract.

Alternate three additions of the flour mixture with two of the buttermilk, starting and ending with dry, mixing on low only until the flour disappears and pulsing the mixer.

Scrape the bowl thoroughly and give it one quick fast mix to finish, blended but not over-mixed.

Weigh the batter into the three pans and smooth it out from the centre with an offset spatula, right up flush with the sides.

Set two pans on one rack on opposite sides and the third centred on the other rack, for air circulation; put them in one at a time, closing the door between, so the oven temperature does not drop.

Bake at 350F for 30 to 35 minutes total, rotating after 25; do not disturb the cakes in the first half of baking or they fall and stay dense.

Break up the unsweetened chocolate and melt it over barely simmering water, then pull it off and let the residual heat finish it gently.

Beat the colder cream cheese alone with a pinch of salt until smooth, creamy and mostly free of lumps.

Add the butter a couple of tablespoons at a time.

Add the whole pound of powdered sugar at once, drape a towel around the mixer and pulse on the lowest speed until contained, then mix and whip, without over-whipping.

Add the cooled chocolate and mix on medium to medium high until completely smooth, scraping the sides.

If the frosting is over-beaten, melt about a quarter cup of it in the microwave and mix it back in.

Level each layer with a serrated knife held parallel to the surface, rotating the cake and letting the knife move through without forcing it.

Set the first layer cut side down, spread approximately one cup of frosting, and place the next layer at eye level, adjusting before any more frosting goes on.

Frost the whole cake in a very thin crumb coat, working from the top down the sides so gravity helps, then scrape the excess with a bench scraper.

Chill the crumb coat down, then add the final frosting, letting it fall over the sides and swirling it rustically.

Cover the whole cake in sprinkles, throwing them at the sides, then slide the parchment strips out around the side of the stand.