Preheat oven to 375 degrees. Line a standard 12-cup muffin tin with paper liners. Set aside.
Whisk together flour, baking powder, and salt in a medium bowl. In the bowl of an electric mixer fitted with the paddle attachment, cream butter and 3/4 cup sugar until light and fluffy. Add egg and egg yolk, and vanilla; mix until well combined. Reduce speed to low; alternate adding reserved flour mixture and milk, beginning and ending with flour. Gently fold in berries (or other mix-ins) using a rubber spatula.
Divide batter evenly among prepared cups. In a small bowl, stir together remaining 1/4 cup sugar and mace. Sprinkle evenly over batter. Bake until light golden brown, about 25 minutes, rotating halfway through baking time. Cool in pan on a wire rack 15 minutes before turning out muffins. Serve warm or at room temperature.