Preheat oven to 350°F (180°C). Butter sides of two 9-inch (23 cm) round metal cake pans and line bottoms with parchment paper.

Sift cocoa into a bowl; gradually whisk in milk until smooth; set aside.

In another bowl, whisk together flour, baking powder, baking soda and salt.

In a large bowl, using an electric mixer, beat sugar and butter until light and fluffy. Beat in eggs, one at a time, beating well after each addition; beat in sour cream and vanilla. Using a wooden spoon, alternately stir in flour mixture and cocoa mixture, making 3 additions of flour and 2 of cocoa, until blended.

Divide between prepared cake pans; smooth tops. Bake for about 30 min or until cake begins to pull away from the side of pans and a tester inserted in center comes out clean. Let cool in pans on a rack for 15 minutes. Invert onto rack and remove pans and parchment paper. Let cool completely.

Whipped Ganache Frosting: Place chocolate in a large, heatproof bowl. In a saucepan, bring cream just to a boil over medium-high heat, stirring occasionally. Pour over chocolate in bowl and let stand for 2 min or until chocolate is melted; stir until smooth. Let cool for 30 to 60 min, until slightly thickened and at room temperature, but not solid.

Using an electric mixer, beat ganache until whipped and just thick enough to spread. In a bowl, lightly mash 1 cup (250 mL) of the raspberries. Add about 1/3 of the whipped ganache to berries and fold until combined.

Place 1 cake layer, domed side up, on a serving plate. Spread raspberry ganache over cake, leaving 1/2 inch (1 cm) border. Place second cake layer, domed side down, on top, pressing lightly. Frost sides of cake thinly with ganache, then frost top. Garnish with remaining raspberries. Serve immediately or refrigerate for up to 1 day. If refrigerated, let stand at room temperature for 15 min before cutting.

Rinse the raspberries and pat them dry before using. Frozen raspberries don’t work well in this cake since they add too much moisture.

Use the best quality chocolate you can find for this frosting. Use chocolate with 65 to 70% cacao for the best texture and flavour. If the percentage isn’t indicated, make sure cocoa liqueur or cocoa mass is the first ingredient in the list on the label.

When frosting the cake, if your room is cool, dip your palette knife or spatula in warm water and wipe dry frequently to prevent frosting from getting too firm.

Brush cake layers with raspberry or chocolate liqueur before assembling the cake. Use a mixture of red and golden raspberries or blackberries for the garnish.