Preheat the oven to 350°F.

In a large bowl, whisk together 3 cups all-purpose flour, 1 1/2 cups granulated sugar, 1 teaspoon baking powder, and 1/2 teaspoon baking soda.

Cut in 1 cup (1 stick) butter into the dry mixture until it resembles small pebbles. Form a well in the center of the mixture and set the bowl aside.

In a small bowl, whisk together 2 eggs (slightly beaten), 1 cup buttermilk, and 1 teaspoon vanilla extract.

Pour the egg mixture into the well in the flour mixture and stir just until the dry ingredients are moistened. The batter will be lumpy — do not overmix.

Spoon half of the batter into an ungreased 9 x 11-inch baking pan and spread it into an even layer.

Evenly drizzle or spoon prepared berry sauce over the first layer of batter.

Drop the remaining batter in mounds over the berry sauce (use a spoon to place dollops), gently spreading or smoothing the dollops as desired so some berry sauce shows through.

Bake for 30–40 minutes, until the top is lightly golden and a toothpick inserted into the cake portion (avoiding large areas of sauce) comes out clean or with a few moist crumbs.

Remove from the oven and let cool slightly in the pan before slicing and serving.