For the Cake• ½ cup unsalted butter softened (113g)• 8 oz cream cheese softened (225g)• 1 cup light brown sugar packed (200g)• ½ cup granulated sugar (100g)• 2 large eggs• 1 ½ teaspoon vanilla extract• 2 ½ cups all-purpose flour (335g)• 2 teaspoons baking powder• 1 teaspoon cornstarch• ½ teaspoon salt• ½ cup buttermilk (120ml)
Sprinkle streusel evenly over batter then bake on 350F for 40-50 minutes(check doneness with a toothpick inserted in center, it should come out clean).