Prep the pan: Heat oven to 350°F (175°C). Line an 8x8-inch pan with parchment, leaving overhang for easy lifting. Lightly grease.

Melt the butter and chocolate: In a heatproof bowl, microwave butter and chocolate in 20–30 second bursts, stirring each time, until smooth. Let cool 2–3 minutes so it’s warm, not hot.

Sweeten the base: Whisk in erythritol or allulose until glossy and mostly dissolved. If using espresso, whisk it in now.

Add eggs and vanilla: Whisk in eggs one at a time until the batter thickens and looks shiny. Stir in vanilla. Don’t overbeat.

Fold in dry ingredients: Sift in almond flour, cocoa, salt, and baking powder (if using). Gently fold until just combined. Batter will be thick.

Chocolate chips: Fold in sugar-free chips if using. Spread batter into the prepared pan, smoothing the top.

Bake: Bake 18–22 minutes until the edges look set and a toothpick comes out with a few moist crumbs. For ultra fudgy, start checking at 18 minutes.

Cool completely: This is key. Cool in the pan on a rack at least 45–60 minutes. Brownies firm as they cool.

Slice cleanly: Lift out using parchment. Use a hot, sharp knife, wiping between cuts, to get neat squares.