Enjoy with whipped cream or Brennan's Vanilla Ice Cream.
Make the topping: In a small bowl blend together the butter, the sugar, the flour, the cinnamon, and the nutmeg until the mixture resembles coarse meal and chill the topping while making the batter.
Make the batter: In small bowl with an electric mixer cream together the butter and the sugar and beat in the vanilla. In a small bowl stir together the baking powder, the flour, and the salt, beat the flour mixture into the butter mixture alternately with the eggs, 1 at a time, beating well after each addition, and fold in the blueberries and the nectarines.
Spread the batter in a well-buttered 10 by 2 inch round cake pan or 2 quart baking pan, sprinkle the topping evenly over it and bake the buckle in the middle of a preheated 350F oven for 45 to 50 minutes, or until a tester comes out clean and the topping is crisp and golden. Server the buckle with whipped cream.