Preheat the oven to 350º F. Prepare a 9x13 baking dish by spraying with nonstick baking spray, such as Baker's Joy, or by buttering and lightly flouring, being sure to shake out any excess flour.
Prepare the Vanilla Cake Recipe as instructed. Pour the Vanilla Cake batter into the prepared baking dish and top with the blueberries.
Whisk together the flour, baking powder, brown sugar, and salt in a medium bowl. Pour in the melted butter and lightly press together the butter with the flour mixture until it forms coarse crumbs. Sprinkle the crumb topping on top of the blueberries.
Bake until the coffee cake is golden brown and a toothpick inserted in the center comes out clean with just a few moist crumbs attached, about 30 minutes. Allow the blueberry coffee cake to cool for about 10 minutes before slicing and serving.
Store covered in the refrigerator overnight, if needed.
Make-Ahead: While this blueberry coffee cake is best served the day it is prepared, you may keep it in the refrigerator overnight covered tightly with plastic wrap.