In a separate bowl, whisk together the egg, milk, and butter and stir in the reserved peach mixture. Mix the egg/peach mixture into the flour mixture until just moistened. (Do not over-mix.) Gently fold in the raspberries.
Fill greased muffin cups 3/4 full and bake for 20 to 25 minutes or until golden brown. Let cool on a wire rack. Serve.