This keto brownie in a mug is gooey and decadent, and serves just one person. It's the perfect single-serve dessert when you need chocolatey goodness but you don't want the leftovers.
In a small microwave safe bowl, melt the butter in the microwave. Stir in the powdered sweetener until well combined, then stir in the egg and vanilla extract.
Add the almond flour, cocoa powder and baking powder, then add water and stir until the mixture is smooth.
Transfer the batter to a small (4-ounce) ramekin and sprinkle with chopped nuts, if desired.
To bake in the oven (or toaster oven)
Preheat the oven to 325ºF and bake the brownie 10 to 15 minutes, depending on how gooey you want it to be.
To bake in an air fryer
Preheat the air fryer to 325ºF and bake the brownie 7 to 9 minutes, depending on how gooey you want it to be.
To bake in a microwave
Microwave on high in 15 to 30 second increments, stopping the microwave in between so that it doesn't spill over. A total of 45 to 60 seconds should be enough.