In a saucepan, melt butter. Stir in brown sugar, flour, cinnamon and nutmeg until smooth. Add apples; cook over medium-low heat for 10 minutes or until tender, stirring frequently. Remove from heat; stir in nuts. Cool. In a bowl, cream butter and sugar. Add eggs, one at a time, beating well after each. Beat in vanilla. Combine dry ingredients; add to creamed mixture alternately with sour cream. Spoon 1/4 cupfuls of batter into greased jumbo muffin cups. Spoon apple mixture into the center of each (do not spread). Top with remaining batter. Sprinkle with cinnamon-sugar. Bake at 350° for 25-27 minutes or until muffins test done. Cool for 5 minutes before removing from pans to wire racks. Yield: 1 dozen jumbo muffins or 2 dozen regular muffins. Note: If using regular-size muffin cups, fill cups half full with batter; add a rounded teaspoonful of apple mixture and remaining batter. Bake for 16-18 minutes.