Preheat the oven to 350 degrees F. Butter and flour a 9-inch round baking pan.
For the streusel:
To make the topping, in a medium bowl, combine the sugars, cinnamon and nutmeg. Add the melted butter then the flour. Mix until it resembles coarse crumbs.
For the cake:
In a medium bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.
Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment on high speed for 4 to 5 minutes, until light.
Reduce the speed to low and add the eggs 1 at a time, then add the vanilla, lemon zest, and yogurt.
With the mixer on low speed, add the flour mixture to the batter until just combined.
Fold in the berries and stir with a spatula to be sure the batter is completely mixed.
Add the batter into the prepared pan and spread it out with a knife.
Using your fingers, crumble the topping evenly over the batter.
Bake for 40 to 50 minutes, until a cake tester comes out clean (mine cooked in 50 minutes).
Cool completely. Top with fresh berries and sprinkle confectioners' sugar.