For the citrus cake:
1 cup (2 sticks) unsalted butter, at room temperature, plus more for the pans
2 1/2 cups all-purpose flour, spooned and leveled, plus more for the pans
Grated zest of two oranges
Grated zest of two lemons
1 1/2 teaspoons baking powder
1/4 teaspoon baking soda
1/2 teaspoon salt
1 1/2 cups sugar
2 teaspoons pure vanilla extract
3 large eggs, at room temperature
1 cup whole milk

For the lemon curd filling:
4 large eggs
1 cup sugar
1 tablespoon finely grated lemon zest
1/2 cup fresh lemon juice
Pinch of salt
1/2 cup (1 stick) unsalted butter, cut into pieces

For the fresh orange-lemon frosting:
2 cups (4 sticks) unsalted butter, at room temperature
2 tablespoons finely grated lemon zest
2 tablespoons fresh orange juice
16 ounces confectioners’ sugar (about 3 3/4 cups), sifted
Pinch of salt