Lightly grease thirty-six 1-3/4-inch muffin cups or line with paper bake cups; set aside.

For topping: In a medium mixing bowl, beat cream cheese, granulated sugar, 1 tablespoon flour and the egg yolk with an electric mixer on medium speed until blended. Fold in chocolate pieces; set aside.

For muffin: In a large bowl, stir together 1-3/4 cups flour, brown sugar, cocoa powder, baking powder, cinnamon, salt and baking soda. Make a well in center of flour mixture; set aside.

In a small bowl, combine egg, milk, oil and vanilla. Add egg mixture all at once to flour mixture. Stir just until moistened (batter should be lumpy). Fold in nuts.

Spoon batter into prepared muffin cups, filling each two-thirds full. Spoon cream cheese topping on top of the batter in each cup. Bake in a 400 degree F oven about 12 minutes or until edge springs back when lightly touched (do not touch cream cheese topping). Cool in muffin cups on a wire rack for 5 minutes. Remove from muffin cups. Serve warm or at room temperature. Cover; store in refrigerator. Makes 36 mini-muffins.

Lightly grease twelve 2-1/2-inch muffin cups or line with paper bake cups; set aside. Prepare batter as above and spoon into muffin cups. Bake in 400 degree F oven about 18 minutes or until edge of muffin springs back when lightly touched. Serve as above.