Preheat the oven to 400 F (200 C). Line 16 cups of two standard muffin pans with paper liners or grease with nonstick cooking spray.
In a small bowl, whisk together the flour, the 1/2 cup (3oz/100 g) sugar, baking powder, and salt. In a large bowl, whisk together the milk, eggs, and butter until blended. Using a rubber spatula, stir in the flour mixture just until evenly moistened. Gently fold in the peach and raspberries just until evenly distributed. Do not overmix.
Divide the batter among the prepared muffin cups, filling each three-fourths full. Sprinkle each with the sliced almonds and the 1 tablespoon sugar, dividing evenly.
Bake until golden and a toothpick inserted into the center comes out dry, 25–30 minutes. Transfer the pan to a wire rack and let cool for 5 minutes. Remove the muffins from the pan and let cool on the rack. Serve warm or at room temperature.