This is a basic muffin recipe. You can vary the taste according to which fruit you choose to use. Other combinations are Strawberry, Cranberry/Orange, and Blueberry/Lemon. It may be necessary to use more flour depending on which fruit you use.
Prepare muffin cups by spraying with non cooking spray or lining with paper muffin cup liners.
Mix together all streusel ingredients with a fork to make a crumbly mixture.
For the batter, whisk together the oil, brown sugar, zest and egg.
Stir in the buttermilk and vanilla.
Stir together 2 1/2 cups flour, salt, baking powder, soda and cinnamon in a bowl.
Add to the wet ingredients and blend.
Fold in your desired fruit.
The use of frozen fruit may help firm up the batter.If the batter seems too loose, add 1/4 cup more flour to make the batter stiffer.
Fill the muffin cups to the top.
Sprinkle streusel topping over each muffin evenly.
Bake for 15 minutes, lower the oven temperature to 350*F and bake for another 12 to 15 minutes or until the muffins spring back when pressed lightly.
Let cool in pan for 5 minutes before unmolding onto wire racks.
NOTE: Fruit variations: Here is a list of what you can use in this recipe: Rhubarb, fresh or frozen, diced, Cranberries, frozen, coarsely chopped, Blueberries, frozen or semifrozen, Apples, diced, peeled or not, Bananas, chopped (add a pinch nutmeg), Frozen raspberries, Frozen strawberries, chopped, dried sour cherries, cranberries or raisins, plumped and patted dry, Strawberry and Rhubarb combination, Apple and cranberry combination, Rhubarb and apple combination.