Preheat oven to 350°F/180°C. Line (or grease and dust with cocoa) a muffin pan, set aside.
Add almond flour, flaxseed meal, coconut flour, baking powder and xanthan gum to a medium bowl. Whisk until thoroughly combined, set aside.
Add butter, heavy cream, cocoa powder and salt to a large heatproof bowl. Melt over a water bath whisking constantly (or use the microwave in small bursts). Remove from heat and allow the mixture to cool slightly... so as not to scramble the eggs!
Add in the sweetener and one egg at a time, whisking well after each one until completely incorporated. The texture should appear smooth and thick, with all the sweetener dissolving into the mixture (if using erythritol, granules will remain). Add the flour mixture, whisking vigorously until fully blended (about a minute). Divide the batter into prepared muffin pan.
Bake for 12-14 minutes if you like your keto chocolate muffins extra fudgy (they'll be set, but still jiggly), and for medium fudgy-ness 15-17. Always keep in mind, however, that your muffins will continue to cook while cooling.
Sprinkle with flaky sea salt (optional, but highly suggested) and allow to cool for at least 15-20 minutes in the muffin pan. They'll be particularly fragile right out of the oven, so you need to let them set a bit.
Keep stored in an airtight container for 3-4 days. And do note that imho these guys are *always* best served warm. Vanilla ice cream highly suggested.
*Psyllium husk powder can be used in place of the golden flaxseed meal, but do expect denser results. **Your choice in sweetener will affect the texture quite a bit. Think xylitol and allulose (no aftertaste, softer and fluffier texture), Lakanto (barely any aftertaste, denser texture). And regarding the amount, I use 1/3 cup but feel free to use even up to 2/3 cup (particularly with allulose, which is 30% less sweet).Fun fact: it might also be my taste buds here, but I’ve noticed that stevia-based sweeteners (such as Pyure) don’t work so great when chocolate is involved as the aftertaste is accentuated. So I cannot recommend enough that you don’t use stevia here!