Preheat the oven to 350°F (175°C)
Grease or line a cake pan
Mix 2 cups whole wheat flour, 1 teaspoon baking soda, and 1 teaspoon cinnamon
In another bowl, whisk 1 cup unsweetened applesauce, 1/2 cup peanut butter, 2 eggs, and 1/4 cup honey
Combine the wet and dry ingredients
Add 1/2 cup grated carrot or mashed banana if desired
Pour the batter into the prepared pan
Bake for 25 to 30 minutes
Check doneness with a toothpick
Let the cake cool completely
Frost with plain mashed sweet potato, plain Greek yogurt, or dog-safe frosting
Decorate with dog-safe treats if desired
Serve a small portion to your dog
Store leftovers in the refrigerator