Brew 12 ounces of strong, hot coffee using your usual method: drip machine, French press, or pour-over all work well.
Pour the hot coffee into a blender. Add the butter, the MCT oil, and the pinch of salt.
Blend on high for 20 to 30 seconds, until the drink turns pale, creamy, and frothy on top. Be careful with hot liquid in a blender: hold the lid down firmly with a towel, and start on low before going to high.
Taste and adjust. Add sweetener if you want it, or a splash more coffee if the cup tastes too rich.
Pour into a warmed mug right away and drink while it is hot and frothy. The foam settles if the cup sits too long, so do not let it wait.