This is my recipe for muffins. They are very lite and cake like. I add cinnamon or other spices, depending on the fruit. I don't add spices with blueberries, sometimes I'll add some lemon or orange zest, but they always get streusel.
3 cups cake flour
1 teaspoon baking soda
2 teaspoons baking powder
1 cup sugar
1/4 teaspoon salt
1 cup sour cream
1 teaspoon vanilla
1 large egg
1/2 cup vegetable oil
2 cups fruit (optional)
1/2 cup chopped nuts (optional)
Streusel topping (optional) 1/2 cup all-purpose flour, 1/4 cup packed sugar (or brown sugar) pulse in the food processor with 1/4 cup of cold, cubed unsalted butter until light, like fresh snow.
Preheat oven to 350°.
Sift the flour, baking soda, and baking powder into a large bowl. Add the sugar and salt; mix, and set aside. Whisk all the wet ingredients together in another bowl.
Add wet ingredients to the dry mixture and mix with a spatula, just until combined. Add fruit and nuts, and fold in gently. Don't over mix. It will be lumpy.
Makes 15-16 regular size muffins. Line or grease muffin tins and fill with batter up to 1/2" from the top. Sprinkle the streusel. Bake for 20 minutes, until golden-brown.