Spiced Plum Upside-Down Cake with Oats Recipe

Ingredients

• 1 cup rolled oats
• 1/2 cup boiling water
• 1 cup brown sugar
• 1/2 cup butter, softened
• 1/2 cup white sugar
• 2 eggs, room temperature
• 1 1/2 teaspoons vanilla extract
• 1 1/2 cups whole wheat flour
• 1 1/2 teaspoons baking soda
• 1 teaspoon ground cinnamon
• 1 teaspoon ground nutmeg
• 1/2 teaspoon sea salt
• 1/4 teaspoon ground allspice
• 2 tablespoons butter
• 1/4 cup raw sugar
• 1/4 teaspoon ground cinnamon, or more to taste
• 1 1/2 cups diced plums