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

Make the brownie batter. In a bowl, whisk melted butter and sweetener until smooth. Add eggs and vanilla; whisk until glossy. Sift in almond flour, cocoa, coconut flour, baking powder, and salt. Stir just until combined. Fold in chocolate chips if using. Spread evenly into the pan.

Make the cookie dough. In another bowl, cream softened butter with the sweetener until light and slightly fluffy. Beat in the egg and vanilla. Add almond flour, coconut flour, baking soda, and salt. Mix until a soft dough forms. Stir in chocolate chips.

Layer it up. Dollop the cookie dough over the brownie layer in small mounds. Use damp fingers or a spatula to gently spread and connect the mounds, covering most of the surface. A few gaps are fine; the dough will spread.

Bake to perfection. Bake for 22–28 minutes, until the cookie top is golden at the edges and set in the center. The brownie layer should still feel soft underneath. If using allulose, check a bit earlier as it browns faster.

Cool and set. Remove from the oven and sprinkle with flaky sea salt if you like. Cool in the pan for at least 45–60 minutes. For clean slices and the fudgiest texture, chill for 30 minutes before cutting.

Slice and serve. Lift out using the parchment and cut into 16 squares. Serve slightly warm or at room temperature. They pair well with unsweetened whipped cream or a scoop of keto vanilla ice cream.