Recipe by @keto.anghellic
I made the cake as directed, with 1 tbsp butter and 1 egg. I cooked it for 1:15 then I let it sit in the mug for a couple minutes before I popped it out and sliced it into thirds. I let it cool a bit while I made the frosting.
I didn't measure, I just whipped together equal amounts of butter and cream cheese, both softened. A couple squeezes of fresh lemon juice, and powdered sweetener.
After I assemble the cake, I sprinkled on some lemon zest for an extra zing.