2 cups Southern soft-wheat all-purpose flour (such as White Lily or Martha White)
2 tsp baking soda
1/2 tsp salt
3 ounces (3 squares) unsweetened chocolate
8 ounces (1 cup or 2 sticks) unsalted butter, softened
1-1/2 cups firmly packed light brown sugar
2 large eggs
1 cup whole-milk buttermilk (or plain whole-milk yogurt thinned with milk to buttermilk consistency)
1 tsp vanilla extract
Old-Fashioned Dark Fudge Frosting (recipe follows)
Recipe
Position a rack in the center of the oven. Preheat oven to 350° F. Butter and flour two 9-inch layer cake pans. Whisk or sift together the flour, baking soda and salt. Melt chocolate in a double boiler over simmering water or in a microwave at half-power; remove chocolate from heat and keep warm.
Cream the butter, then add sugar and continue to cream until fluffy and light. Beat in eggs, one at a time, then stir in melted chocolate. Mix in the flour mixture and buttermilk a little at a time, alternating, beginning and finishing with flour mixture. Stir in vanilla. Divide batter between the prepared pans, tap them lightly on the counter to remove any air bubbles, and bake about 20 minutes, or until a straw or toothpick inserted in the center comes out clean.
Cool the cakes in the pan on wire racks. While they cool, make the frosting. Invert one cooled cake layer over a cake plate and carefully remove the pan. Cover it thickly with about one-third of the frosting. Invert second cake layer over first layer, remove the pan, then frost top and sides with the remaining frosting. Let the frosting set before cutting, at least 1 hour.