Prep the pan: Heat oven to 350°F (175°C). Line an 8x8-inch pan with parchment, leaving overhang for easy lifting.
Melt butter and chocolate: In a heat-safe bowl, melt the butter and sugar-free chocolate together (microwave in 20–30 second bursts, stirring, or use a double boiler). Cool 2–3 minutes.
Whisk in sweetener and vanilla: Stir in your keto sweetener and vanilla until glossy.
If using espresso powder, add it now.
Add eggs: Whisk in eggs one at a time until the mixture looks thick and shiny. Don’t overbeat.
Combine dry ingredients: In a small bowl, whisk almond flour, cocoa powder, baking powder, and salt. Sift if lumpy.
Fold to finish: Gently fold dry ingredients into the wet mixture until just combined.
Stir in nuts or chips if using.
Bake: Spread batter in the pan. Bake 18–22 minutes, until the edges are set and the center is slightly soft. A toothpick should come out with a few moist crumbs.
Cool completely: Let brownies cool in the pan at least 30–45 minutes, then lift out and slice.
For the cleanest cuts, chill 20 minutes first.