1) Preheat the oven to 350°F. Lightly grease a 9" round cake pan.
2) To make the cake: In a medium-sized mixing bowl, beat together the butter and sugar.
3) Beat in the egg and vanilla.
4) Stir in the baking powder, salt, and nutmeg.
5) Add the flour in three additions, stirring it in alternately with the milk, and beginning and ending with the flour. Set the batter aside while you make the topping.
6) To make the topping: Mix all of the ingredients until crumbly. Don't over-mix, or you'll get a smooth paste, rather than crumbs.
7) To assemble the buckle: Spread half the batter (about 10 ounces) in the prepared pan. Layer with the peach slices.
8) Fold the blueberries into the remaining batter, and dollop it on top; a tablespoon cookie scoop works well here.
9) Sprinkle the topping over the batter.
10) Bake the buckle for 50 minutes to 1 hour, or until it's a deep golden brown and a cake tester or toothpick inserted into the center comes out clean.
11) Remove the buckle from the oven, and cool it on a rack. Serve warm, or at room temperature. Store at room temperature, wrapped in plastic, for several days; freeze for longer storage.
Yield: 9 to 12 servings.