Blend softened butter and Sweet Blend together in a mug or dessert bowl.
Add egg yolk and stir well.
Add cocoa, baking powder, salt, and cream; stir until combined.
Add almond flour and mix with fork until well blended.
Sprinkle walnuts on top of batter.
Microwave on high for 1 min. 30 sec. or until muffin is done.