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

Mix the dry ingredients: In a medium bowl, whisk 1 1/2 cups almond flour, 1 1/2 tablespoons coconut flour, 1/2 cup unsweetened cocoa powder, 1 teaspoon baking powder, 1/2 teaspoon salt, and 1/2 teaspoon espresso powder (optional) until smooth and lump-free.

Cream the butter and sweetener: In a large bowl, beat 1/2 cup melted and slightly cooled unsalted butter with 2/3 cup granular erythritol (or monk fruit/erythritol blend) until combined. It won’t get fluffy like sugar, and that’s fine.

Add eggs and vanilla: Whisk in 2 large eggs plus 1 extra yolk and 2 teaspoons vanilla extract. Mix until glossy and thick.

Combine the batter: Add the dry ingredients to the wet mixture. Stir until just combined. If the batter seems very thick, add 1–2 tablespoons heavy cream to loosen slightly. Fold in 1/3 cup sugar-free chocolate chips if using.

Bake: Spread the batter evenly in the prepared pan. Bake for 18–22 minutes, until the edges are set and a toothpick inserted in the center comes out with a few moist crumbs. Do not overbake.

Cool completely: Let the brownies cool in the pan on a rack. This keeps them fudgy and prevents crumbling.

Make the fudge frosting: In a small saucepan over low heat, melt 3 tablespoons butter with 1/4 cup heavy cream. Whisk in 1/4 cup unsweetened cocoa powder until smooth. Remove from heat and whisk in 2/3–3/4 cup powdered erythritol (to taste) and 1 teaspoon vanilla. The frosting should be pourable but thick.

Frost and set: Pour the warm frosting over the cooled brownies and spread evenly. Let it set at room temperature for 30–45 minutes, or chill for 15–20 minutes if you’re impatient.

Slice and serve: Lift the brownies out using the parchment. Slice into 16 squares with a sharp knife, wiping the blade between cuts for clean edges.