Lemon Layer Cake with Lemon Curd & Vanilla Buttercream

Make the lemon curd first. Whisk sugar, zest, lemon juice, eggs, yolk, and salt in a saucepan. Cook over medium-low heat, stirring constantly, until thick enough to coat a spatula and about 170°F, 7–10 minutes.

Remove curd from heat and whisk in butter a few pieces at a time. Strain if desired, cover the surface directly, and chill until completely cold, at least 2 hours.

Heat oven to 350°F. Grease and parchment-line three 8-inch round pans.

Whisk flour, baking powder, baking soda, and salt.

Beat butter, sugar, and lemon zest until pale and fluffy, about 3 minutes.

Beat in eggs one at a time, then vanilla. Combine milk and lemon juice separately.

Add dry ingredients in three additions, alternating with the milk-lemon mixture in two additions. Mix only until combined.

Divide among pans and bake 21–26 minutes, until centers spring back and a tester is clean.

Cool in pans 10 minutes, then turn out and cool completely.

For vanilla buttercream, beat butter until creamy. Gradually beat in confectioners' sugar, then vanilla, salt, and enough cream for a smooth spreadable consistency.

Place the first cake layer down and pipe a buttercream dam around the edge. Spread a thin even layer of cold lemon curd inside the dam. Repeat with the second layer and top with the third.

Crumb-coat, chill 15 minutes, then frost with remaining vanilla buttercream. Chill at least 30 minutes before slicing.