Dust this cake with powdered sugar and serve with fresh raspberries and a dollop of light whipped topping, if desired.
Preheat oven to 350°F. Coat a tube pan with canola cooking spray and dust lightly with flour. Place the raspberry preserves in a small microwave-safe bowl and heat on high for 15 seconds or until softened.
Add whole-wheat and white flours, sugar, sugar substitute, cocoa, baking soda, and salt to large mixing bowl and beat on low to blend well. Stop mixer and add margarine, liqueur, sour cream, eggs, vanilla, and softened preserves all at once. Beat on medium speed for two minutes, scraping sides of mixing bowl after a minute.
Pour batter into prepared pan and bake for 50-60 minutes, or until cake tester inserted in center comes out clean. Cool in pan 10 minutes, then remove cake from pan and place on serving plate to cool completely. When ready to serve, dust powdered sugar over the top. Serve with fresh raspberries and a dollop of whipped topping or whipping cream. if desired.