In a large bowl, whisk together the oat flour, baking powder, salt, and sugar. Lightly whisk the egg separately, then stir in the beaten egg, milk, and butter. Gently fold in the raspberries.
Spoon the batter evenly into the muffin tin (fill each cup about two-thirds full). Preheat the oven to 375℉ and let the batter rest while the oven heats. Bake the muffins for 20-25 minutes, until a tester comes out clean.
Place the muffin tin on a wire rack to cool for about 10 minutes, then gently turn out the muffins onto the rack to cool completely.