1 cup (250 mL) butter, softened
1-1/2 cups (375 mL) granulated sugar
1 tsp (5 mL) vanilla
2 cups (500 mL) all-purpose flour
1/2 cup (125 mL) cocoa powder
1 tsp (5 mL) each baking powder and baking soda
1/4 tsp (1 mL) salt
1-1/2 cups (375 mL) buttermilk
1-1/2 cups (375 mL) Unsalted butter, softened
1/2 cup (125 mL) whipping cream
1 tbsp (15 mL) vanilla
3 cups (750 mL) icing sugar
6 oz (175 g) Unsweetened chocolate, chopped, melted and cooled
Chocolate Cake: Grease two 8-inch (2L) springform pans or grease two 8-inch (1.2 L) round metal cake pans and line bottoms with parchment or waxed paper. Set aside.
In large bowl, beat butter with sugar until light and fluffy. Beat in eggs, 1 at a time; beat in vanilla. In separate bowl, sift together flour, cocoa, baking powder, baking soda and salt. With wooden spoon, stir into butter mixture alternately with buttermilk, making 3 additions of dry ingredients and 2 of buttermilk. Spoon into prepared pans, smoothing tops.
Bake in centre of 350°F (180°C) oven for 30 to 35 minutes or until cake tester inserted in centre comes out clean. Let cool on racks for 20 minutes. Remove from pans; let cool completely on racks. (Make-ahead: Wrap layers separately in plastic wrap and refrigerate for up to 1 day or overwrap with heavy-duty foil and freeze for up to 2 weeks.)
Cut each cake horizontally into 2 layers.
Chocolate Icing: In bowl, beat butter until fluffy; gradually beat in cream. Beat in vanilla. Beat in icing sugar, 1 cup (250 mL) at a time. Beat in melted chocolate until fluffy and smooth.
Place 1 layer, cut side up, on cake plate. Slide strips of waxed paper between cake and plate. Spread cut side with about 3/4 cup (175 mL) of the icing; cover with remaining half, cut side down. Spread top with another 3/4 cup (75 mL) of the icing. Repeat with remaining layers, spreading remaining icing over side and top. Remove paper strips. (Make ahead: Cover loosely and refrigerate for up to 2 days. Let come to room temperature before serving.)