Prepare streusel topping: In a small bowl, cut softened butter into streusel mix until well blended. Set aside.
In a medium-sized bowl, place 2 cups muffin mix. Make a well in the center of mix and add oil, egg and vanilla. Whisk liquids briskly until egg is blended.
Add the milk and stir entire mixture until just evenly moistened.
Fill muffin cups about 1/3 full with batter. Top with 1 teaspoon of streusel mix.
Place another spoonful of batter into each cup. Sprinkle remaining streusel mix on top of each muffin.
Bake for 15 minutes. Do not overbake.
Menu Suggestions
Variations:
Blueberry: Add 3/4 cup blueberries (fresh, frozen or dried)