Generously grease and flour three 9-inch round cake pans. Set the pans aside.
Strain the raspberries through a fine-mesh sieve if you don’t want the seeds in your cake.
Place the cake mix, raspberries and their juice, sour cream, oil, and eggs in a large mixing bowl. Blend with an electric mixer on low speed for 1 minute. Stop the machine and scrape down the sides of the bowl with a rubber spatula. Increase the mixer speed to medium and beat 2 minutes more, scraping down the sides again if needed. The batter should look well blended.
Divide the batter evenly among the prepared pans, smoothing it out with the rubber spatula.
Bake the cakes until they spring back when lightly pressed with your finger, 25 to 28 minutes.
Remove the pans from the oven and place them on wire racks to cool for 10 minutes. Run a dinner knife around the edge of each layer and invert each onto a rack, then invert again onto another rack so that the cakes are right side up. Allow to cool completely, 30 minutes more.
Meanwhile, prepare the Chocolate Ganache, adding the Chambord, if desired, after all the chocolate has melted.
Place one cake layer, right side up, on a serving platter. Spread the top with ganache frosting. Place the second layer, right side up, on top of the first layer. Spread the top with ganache. Place the third layer, right side up, on top of the second layer and frost the top and sides of the cake. Work with clean, smooth strokes.
Decorate the top attractively with the fresh raspberries, if desired. Place this cake, uncovered or in a cake saver, in the refrigerator until the frosting sets, 20 minutes. Store in the refrigerator for up to 1 week.
Ganache: Place the cream in a small heavy saucepan over medium heat and bring to a boil, stirring. Meanwhile, place the chopped chocolate in a large stainless-steel mixing bowl. Remove the cream from the heat, and pour it over the chocolate. Stir with a wooden spoon until the chocolate is melted. Stir in the liqueur if desired.
To use this ganache as a glaze, let it stand at room temperature for 10 minutes before spooning it over a cooled cake. To use the ganache as a frosting, let it stand for 30 minutes at room temperature, or chill it for 10 minutes, until it has thickened enough to spread with a metal spatula.
Makes 1 3/4 C., enough to thinly frost a 2 - 3 layer cake.