Prep the pan and oven. Heat the oven to 350°F (175°C). Grease an 8x8 baking dish with butter or oil, making sure to coat the corners.
Add dry ingredients to the pan. In the pan, whisk together almond flour, cocoa powder, sweetener, baking powder, and salt. Break up any cocoa clumps so the batter mixes evenly.
Add wet ingredients. Crack in the eggs, pour in melted butter, almond milk, and vanilla.
If using espresso powder or cinnamon, add them now.
Mix right in the pan. Use a spatula or whisk to stir until smooth and glossy. Scrape down the sides so no dry pockets remain.
Fold in chocolate chips. Stir in the sugar-free chocolate chips (and nuts if using). Sprinkle a few extra chips on top for a bakery look.
Bake. Slide the pan into the oven and bake for 22–28 minutes.
The edges should be set, and the center should look slightly soft but not jiggly. A toothpick should come out with a few moist crumbs.
Rest and slice. Let the cake cool in the pan for at least 15 minutes. This helps it set into a fudgy texture that slices cleanly.
Serve. Enjoy warm or at room temp.
Add a dollop of whipped cream or a few raspberries for a simple finish.