In a medium microwave-safe bowl, whisk the nut butter and egg together until smooth. Stir in the flax seed meal, cinnamon, baking powder, and salt until well combined.
Divide the mixture between two well greased 4-inch ramekins. Microwave together ramekins on high for 90 seconds. Let cool for a few minutes.
Run a sharp knife around the inside of the ramekins and flip the muffins out onto a wire rack. Slice in half and toast to your liking.
Notes
Storage Information: Once baked in the microwave, remove the muffins from the ramekins and let the cool completely. Then slice them in half and store them in a covered container in the fridge for up to a week. You can also freeze them for several months.