Place the butter in a microwave-safe 4-inch ramekin*. Melt it in the microwave, then allow it to slightly cool.
With a fork, mix in the egg and salt.
Mix in the almond flour, thoroughly mixing until smooth.
Finally, mix in the baking powder.
Microwave for 90 seconds, until puffed and a toothpick inserted in rthe center comes out clean.
Invert the muffin into a cutting board and allow the bottom to air out for a couple of minutes, it will be very moist. If the bottom sticks to the ramekin and the muffin won't come out, carefully loosen it with a spoon.
Cut the muffin crosswise into two slices. Toast in a greased skillet, or in the toaster on the lowest setting. Butter generously and enjoy!
Video
Notes
*The ramekin I use holds about ¾ cup (6 ounces) of liquids. But you want it to be wide and shallow, not small and deep. So the diameter is important here.For the best results, you should toast the muffins on both sides in a buttered skillet. However, as you can see in the video, I sometimes use a toaster on the lowest setting and the results are fine, though not as good as skillet toasting.The leftovers keep quite well in the fridge for 3-4 days. I microwave the muffins, toast them, cool them completely, and then store them in a Ziploc bag in the fridge. The next morning, I briefly reheat them in the microwave and they are perfect.You can also freeze the leftovers for up to 3 months. If stacking them, place a layer of wax paper between them.