Blackberry Plum Upside-Down Cake

Ingredients

• Topping
• 3 tablespoons (43g) unsalted butter, at room temperature
• ⅓ cup (71g) light brown sugar
• 1 cup (170g) blackberries
• 4 large (260g) plums, thickly sliced
• Cake Batter
• 8 tablespoons (113g) unsalted butter, at room temperature
• 1 cup (213g) light brown sugar
• 2 large (113g) eggs
• 1 teaspoon pure vanilla extract
• 1 cup (120g) all-purpose flour
• ¾ (85g) cup whole-wheat flour
• 2 teaspoons baking powder
• ½ teaspoon ground cinnamon
• ½ cup (115g) whole milk
• Whipped cream, as needed for serving