Preheat your oven to 350°F and grease a 9x13-inch baking pan with butter or cooking spray. Line the bottom with parchment paper for easy removal and cleanup.
Whisk together flour, baking powder, and salt in a medium bowl, then set aside. This dry mixture forms your cake base.
Beat softened butter and granulated sugar together until light and fluffy, about 2-3 minutes, then add eggs one at a time. Alternate adding your dry ingredients and sour cream in thirds, beginning and ending with flour, then stir in vanilla extract. Fold in blueberries gently so they stay intact.
Make the streusel by combining brown sugar, cold butter, flour, and almonds with a fork until crumbly. Your blueberry coffee cake family summer recipe topping should resemble coarse breadcrumbs.
Pour cake batter into the prepared pan and spread evenly, then scatter streusel topping across the entire surface. Bake for 40-45 minutes until a toothpick inserted in the center comes out clean or with just a few moist crumbs.
Cool in the pan for 15 minutes before turning out onto a wire rack. The cake will be warm and fragrant—resist cutting for at least another 20 minutes for clean slices.