PREHEAT OVEN TO 350 DEG F. IN A LARGE BOWL, CREAM THE BUTTER, MARGARINE, SUGAR. CREAM UNTIL LIGHT AND FLUFFY. BLEND IN THE EGGS. IN A BOWL, COMBINE SOUR CREAM AND BAKING SODA. SET ASIDE. SIFT CAKE FLOUR, SALT, BAKING POWDER AND NUTMEG TOGETHER. ADD FLOUR MIXTURE AND SOUR CREAM TO BUTTER MIXTURE. DO NOT OVER MIX. IN A LARGE BOWL, COMBINE CRUNCH MIX INGREDIENTS WITH A PASTRY BLENDER. MIX WELL. FOLD IN half CUP CRUNCH MIX WITH MUFFIN MIX. SPOON INTO PAPER CUP LINED MUFFIN TINS. FILL A LITTLE OVER HALF FULL. SPRINKLE REMAINING CRUNCH MIX OVER THE TOP. BAKE FOR 25 MINUTES OR UNTIL GOLDEN BROWN. MAKES dozen MUFFINS.