Gather your ingredients.
In a microwave-safe mug sprayed with nonstick cooking spray whisk together peanut butter and maple syrup until smooth.
Whisk in plant milk, powdered peanut butter, oats, spelt flour (or flour of choice), and brown sugar alternative until it forms a light batter with no clumps. If too thick add additional plant milk in 1 tablespoon increments to thin.
Microwave on high for 1 minute or stop the microwave 10 seconds after you see the cake rising to it maximum height. Remove from the microwave and check the texture – it should be moist and soft, and the top should deflate. If it is not cooked to your liking, cook again in 10-second bursts until done. The longer you cook the denser it will become.