Nonstick cooking spray
9 ounces cake flour, approximately 2 cups
1 teaspoon baking powder
1/2 teaspoon kosher salt
1/2 teaspoon ground ginger
2 ounces unsalted butter, room temperature
5 1/4 ounces sugar, approximately 3/4 cup
1 large egg
1/2 cup whole milk
15 ounces fresh whole blueberries, approximately 3 cups
For the topping:

3 1/2 ounces sugar, approximately 1/2 cup
1 1/2 ounces cake flour, approximately 1/3 cup
1/2 teaspoon freshly ground nutmeg
2 ounces unsalted butter, chilled and cubed