Preheat oven to 375 degrees. Lightly grease a 9-inch skillet or baking pan.

In a small bowl, combine the ingredients for the topping. Work in the butter with a fork or pastry cutter until the mixture has a crumb-like appearance. Set aside.

In a medium bowl, whisk together the flour, baking powder, salt, cinnamon and ginger.

With an electric mixer, beat the butter and sugar in a large bowl until light and fluffy. Mix in the egg and vanilla. Mix in 1/3 of the flour mixture at a time, alternating with the buttermilk (starting and ending with the flour mixture).

Fold in the blueberries, then pour the mixture into to prepared pan. Sprinkle on the streusel in an even layer.

Bake for about 45 minutes, or until golden and a toothpick inserted in the center comes out clean. Cool on a wire rack for at least 30 minutes before serving.