First, combine the almond flour, psyllium husk powder, sea salt, and baking powder. You can combine all the ingredients in a small bowl and then transfer them to a coffee mug at the end. Alternatively, you can combine all the ingredients directly into a tall coffee cup (about 10-12 oz).
Add in the egg. Mix very well. The mixture will be very thick at this point.
Combine boiling water and apple cider vinegar. Add this to the mixture as well. Mix extremely well to incorporate any dry spots. The mixture should bubble quite a bit.
Add in the shredded cheese. Mix well until well combined. Alternatively, you can leave the shredded cheese on top of the dough. Feel free to substitute the shredded cheese with any variety you would like.
Cook for 1 minute and 45 seconds in the microwave. Add an extra 30 seconds if necessary. Carefully remove the mug bread from the coffee cup onto a cutting board. Allow to cool thoroughly (about 4-5 minutes). Then cut the mug bread into 3-4 slices and enjoy immediately.