There's a Chocolate Date Cake here on the recipe link that uses the ground chocolate. I know you didn't mention dates, but thought perhaps you could rework it.

CHOCOLATE DATE CAKE

1 cup walnuts, chopped
1 cup pitted dates, chopped
1 1/2 cups all-purpose flour
1 cup mayonnaise
1 cup hot water
1 tsp. baking soda
1 tsp. vanilla
1/8 tsp. salt
1 cup Ghirardelli ground chocolate

Cover nuts and dates with boiling water into which you've stirred baking soda. Let stand.

Sift flour, measure it, and sift again with sugar and ground chocolate. Add date/nut mixture; mix well. Blend in mayonnaise. Add vanilla and mix thoroughly. Pour into greased and floured 9x13 inch pan.

Bake at 325 degrees for 50-60 minutes.

The cake will keep for 2 weeks. I usually do not frost it, but sprinkled powdered sugar on top.