Ombré Citrus Upside-Down Cake

Ingredients

• Topping
• 3 tablespoons unsalted butter
• ⅓ cup light brown sugar
• 1 Meyer lemon, halved and thinly sliced
• 1 navel orange, halved and thinly sliced
• 1 cara cara orange, halved and thinly sliced
• 1 blood orange, halved and thinly sliced
• Cake
• 2 sticks unsalted butter, softened
• ½ granulated cup sugar
• ½ cup light brown sugar
• 2 large eggs
• 1 teaspoon pure vanilla extract
• 1 cup all-purpose flour
• ¾ cup whole-wheat flour
• 1 teaspoon ground cinnamon
• 1 teaspoon baking powder
• ½ teaspoon baking soda
• ¾ teaspoon salt
• 1½ cups sour cream