Butter the largest mug you have (to stop it overflowing in the microwave). Add the butter, peanut butter and milk into the mug and warm in the microwave for 10 seconds. Stir to combine.

Add the egg and stir to combine. Add the ground almonds, cacao and xylitol and mix until combined.

Centre the mug in the middle of the microwave and cook. Start on a high temp (for a 750W microwave) and cook for three 30 second intervals.The cake will look a bit gooey when it comes out, but allow it to rest for 2mins and it will firm up nicely. Top with Greek yogurt, nut butter or desiccated coconut if you like.