Preheat oven to 350 degrees. Prepare lamb mold.
Beat butter and sugar together until light and fluffy. Add eggs one at a time, beating after each addition. Add vanilla and chocolate and beat on low speed until blended.
Sift flour with baking powder, soda, and salt. Add alternately with milk, beginning and ending with flour mixture and beating just until well blended.
Pour the batter into prepared pan and bake for 55 minutes. (Follow directions in lamb cake tutorial to unmold.)