INGREDIENTS: topping 1 cup (packed) dark brown sugar 1/2 cup sugar 1 1/2 tablespoons ground cinnamon 1/2 teaspoon salt 1 cup (2 sticks) unsalted butter, melted, warm 2 1/2 cups all purpose flour cake 2 1/2 cups all purpose flour 1 teaspoon baking soda 3/4 teaspoon baking powder 1/2 teaspoon salt 3/4 cup (1 1/2 sticks) unsalted butter, room temperature 1 1/2 cups sugar 2 large eggs 1 1/3 cups sour cream 1 teaspoon vanilla extract PREPARATION topping: Mix both sugars, cinnamon, and salt in...