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

Make the brownie batter: In a bowl, whisk melted butter, eggs, erythritol/monk fruit, allulose, and vanilla until glossy and smooth. In another bowl, whisk almond flour, cocoa powder, baking powder, and salt. Fold the dry mix into the wet until just combined. Stir in chocolate chips if using. Spread evenly in the prepared pan.

Make the cookie dough: In a clean bowl, beat softened butter and sweetener until light and fluffy, about 1–2 minutes. Beat in the egg and vanilla. In a separate bowl, whisk almond flour, coconut flour, baking soda, and salt. Add dry ingredients to the wet and mix until a thick dough forms. Fold in chocolate chips.

Layer it up: Dollop the cookie dough evenly over the brownie batter. Gently press and spread to mostly cover the surface. It doesn’t need to be perfect—gaps let the brownie peek through and bake beautifully.

Bake: Bake for 22–28 minutes, until the cookie top is golden and a toothpick inserted in the center comes out with a few moist crumbs. Avoid overbaking to keep the brownie layer fudgy.

Cool completely: Place the pan on a rack and cool at least 1 hour. For cleaner slices and the best texture, chill for 30–60 minutes after cooling.

Finish and serve: Lift the brookies out with the parchment, slice into 16 squares, and sprinkle with flaky sea salt if you like. Enjoy at room temperature or slightly warm.