Preheat the oven to 400°F. Lightly grease the cups of a standard muffin pan; or line with paper baking cups, and grease the paper cups., Whisk together all of the dry ingredients, including the granola., In a separate bowl, whisk together the vanilla, vegetable oil, and buttermilk or whey., Pour the liquid ingredients into the dry ingredients, stirring just to combine., Spoon the batter into the prepared muffin cups, filling them nearly full. A slightly heaped muffin scoop of batter is the right amount., Sprinkle the tops of the muffins with additional granola, if desired., Bake the muffins for 16 to 18 minutes, until a toothpick inserted into the middle of one of the center muffins comes out clean., Remove the muffins from the oven, and after 5 minutes (or when they're cool enough to handle) transfer them to a rack to cool. Serve warm, or at room temperature. Store leftovers loosely wrapped at room temperature.