Berries, peaches, and citrus lend a fruity freshness to this recipe, while sour cream gives richness and a little zing to these tender corn muffins.
Preheat your oven to 400° and set a rack to the middle position. Line the cups of a standard 12-cup muffin pan with paper liners or grease them lightly with butter.
In a large bowl, whisk together the flour, cornmeal, sugars, baking powder, and salt. In a medium-size bowl, whisk together the butter, milk, sour cream, eggs, lemon zest, lemon juice, and orange zest.
Pour the wet ingredients into the dry ingredients, and stir, just until combined. Gently fold in the raspberries and peaches until mixed throughout.
Divide the batter evenly among the prepared muffin cups and sprinkle with demerara sugar, if using. Bake until lightly golden, about 25 minutes. Let cool slightly before unmolding.