Spiced Plum Upside-Down Cake with Oats Recipe

Ingredients

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