If your vegan mug cake is dense, chewy or rubbery in texture, you overcooked it! With mug cakes, it is always better to undercook it slightly as opposed to overcooking it. It's also very important to use the correct sized mug. If you try to cook this in a tall, narrow mug your cake will be extremely thick and very difficult to cook all the way through. Wide and shallow mugs are the best mugs to use for microwaved cakes.