1) Preheat the oven to 350°F. Grease 8 wells of a standard muffin pan, or line with papers.
2) Stir together the dry ingredients in a medium-sized bowl; set aside.
3) Whisk together the melted butter or oil, eggs, milk, and vanilla.
4) Stir the dry mixture into the wet ingredients. Scrape the bottom and sides of the bowl, and continue to mix just until blended - a few lumps will remain.
5) Fold in the berries.
6) Fill the muffin cups almost full. Sprinkle with cinnamon-sugar, if desired.
7) Let the muffins rest for 10 minutes, then bake for 20 to 25 minutes, until a cake tester inserted into the center of a muffin comes out clean.
8) Remove the muffins from the oven, and after 5 minutes transfer them to a rack to cool.
Yield: 8 muffins.