Combine baking mix and sugar in a large bowl; stir in chocolate and nuts. Make a well in center of mixture. Combine half-and-half and remaining 3 ingredients; add to dry ingredients, stirring just until dry ingredients are moistened.
Spoon into greased muffin pans, filling two-thirds full. Bake at 400° for 11 to 12 minutes or until a wooden pick inserted into center comes out clean. Remove from pans immediately.