Preheat the oven to 350 degrees F (177 degrees C). Grease a 8” pan.
Melt the butter and chocolate together in a double boiler, stirring occasionally, until smooth. Remove from heat.
Stir in the vanilla extract.
Add the almond flour, powdered sweetener, cocoa powder, sea salt, and eggs. Stir together until just mixed. Fold in walnuts.
Pour batter into the pan. Smooth the top with a spatula. If desired, sprinkle with chocolate chips and press into the top.
Bake for about 13-18 minutes, until an inserted toothpick comes out almost clean with just a little batter on it that balls up between your fingers. (Don’t wait for it to come out totally clean, and don't worry about any butter pooled on top - just watch the actual brownie part to be super soft but not fluid.)
Cool completely before moving or cutting. There may be some butter pooled on top - do not drain it, it will absorb back in after cooling.
