In a large bowl, cream ½ cup butter (softened) and 1 cup sugar until light and fluffy. Add 2 eggs, one at a time, beating well after each addition.
In another bowl, whisk together 1 cup flour, 1 teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt, 1 tablespoon cocoa powder, 1 teaspoon cinnamon, ½ teaspoon nutmeg, and ¼ teaspoon cloves.
Add the flour mixture to the butter mixture, stirring just until combined.
Stir in 1 cup quick oats, 1½ cups peeled and diced apples, and ½ cup walnuts (if using).
Bake for 24–26 minutes, or until a toothpick inserted into the center comes out clean. Let cool and sprinkle with powdered sugar.
Notes
Check out these tips for how to soften butter quickly if you'd like to get started baking right away.Storage: store in an airtight container at room temperature for several days or in the fridge for up to one week. Types of apples: I like using Granny Smith and/or Honeycrisp apples (preferably, a mixture for more depth of flavor). Golden Delicious, Braeburn, and Pink Lady work well in this cake, too.