Preheat oven to 350 degrees F (175 degrees C). Grease and flour an 8 1/2-inch cake pan.

Melt butter and unsweetened chocolate in a saucepan over medium-low heat.

Remove from heat.

Add hot water and 1 cup sugar, mix well, and let cool.

Whisk together flour, baking soda, salt, and baking powder in a separate bowl.

Whisk egg and vanilla extract into the cooled chocolate mixture.

Add vinegar to milk and mix.

Alternately whisk the milk and flour mixtures into the chocolate mixture until fully incorporated.

Pour batter into the prepared cake pan.

Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

Let cake cool in the pan.

Whip heavy cream and remaining 2 teaspoons sugar until soft peaks form.

Grate bittersweet chocolate and set aside.

Rinse the raspberries.

Run a knife around the perimeter of the cooled cake, and invert the cake onto a plate.

Slice the cake in half, horizontally.

Sprinkle creme de cassis generously on each cut side.

Place the bottom half on a platter, cut side up.

Spread 1/3 of the whipped cream over the cut side of the bottom half.

Stack the top half, cut side up, on the bottom half.

Spread the remaining whipped cream over the top and sides of the cake.

Garnish with raspberries and press grated bittersweet chocolate onto the sides.

Refrigerate until ready to serve.