In a microwave safe container, melt the butter by placing it in the microwave for about 15 to 20 seconds.
Add the egg and whip it until fluffy. Add lots of air by whipping the egg helps make a fluffy texture. Make sure not to skip this step because we didn't add baking powder to this recipe.
Add the remaining dry ingredients to the wet ingredients and mix until it's fully incorporated and smooth.
Spray your mug cake container with non stick cooking spray and add the batter.
The cooking time will depend on the size of your mug or container.
I large microwave safe mug will take 60 to 110 seconds to fully cook.
If you use a small microwave safe mug be sure to divide the batter into two equal parts and cook them separately. Cook small mugs for 60 seconds each.
If you use the small microwave safe silicone container, these will only take 30 seconds to cook because the heart waffle is really small.
After the cake has been fully cooked, add any toppings you want!