Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a mixing bowl, combine the tahini, eggs, erythritol, baking powder, and liquid stevia. Mix well until the ingredients are thoroughly combined.

Add the crushed mixed nuts and sugar-free chocolate to the dough. Stir until they are evenly distributed throughout the dough.

Place spoonfuls of the dough onto the prepared baking sheet, leaving some space between each cookie as they will spread slightly. Alternatively, you can spread the mixture onto the 8-inch square baking pan.

Gently flatten each cookie with the back of a spoon or your hand to your desired thickness. 

Bake in the preheated oven for about 12-15 minutes, or until the edges are golden brown and the cookies are set.

Remove the baking sheet from the oven and let the cookies cool on the sheet for a few minutes. Then transfer them to a wire rack to cool completely.

Once cooled, the keto cookies are ready to enjoy! Store them in an airtight container at room temperature for up to 5 days, or freeze them for longer storage.