Adapted from Martha Stewart's Baking Handbook via 365 Days of Baking
2 sticks (one cup) butter, room temperature, plus more for pan
1½ cups all-purpose flour, plus more for pan
1½ cups cake flour
1 tablespoon baking powder
½ teaspoon salt
1 3/4 cups sugar
2 teaspoons vanilla
1 ¼ cups milk
Preheat oven to 350º. Butter two 9 inch cake pans, line bottoms with parchment. Butter parchment, then dust with flour; set aside. In a bowl, whisk together flours, baking powder, and salt; set aside.
In the bowl of a mixer fit with the paddle attachment, beat the butter and sugar until light and fluffy, about 3 minutes, scraping down the sides of the bowl as needed. Beat in eggs, one at a time, then mix in vanilla. With the mixer on low speed, add the flour mixture in three parts, alternating with the milk and beginning and ending with the flour. Beat until combined after each addition.
Pour batter into prepared pans, and smooth tops with an offset spatula.
Bake until the cake is golden brown and a cake tester inserted in the center comes out clean, 30-35 minutes.
Let cool on racks about 10 minutes, then remove from pans, peel off parchment and allow to cool completely. Make icing.
1 pound semi-sweet chocolate, chopped
6 tablespoons Dutch-process cocoa
6 tablespoons boiling water
3 sticks (1 1/2 cups) of butter, at room temperature
1/2 cup powdered sugar
1 teaspoon vanilla
Gently melt chocolate in microwave, stopping and stirring at 30 second increments till melted and smooth. Set aside to cool to room temperature, about 15 minutes.
Stir together cocoa and boiling water till cocoa is dissolved.
Put butter and powdered sugar in bowl of mixer fit with a paddle attachment. Beat till fluffy, about 2-3 minutes. Add vanilla and mix. Add cooled chocolate and mix till well combined. Add cocoa mixture and beat into frosting.
Frost cake as desired.