Preheat the oven to 180°C / 350°F (160°C / 320°F fan). Line a baking sheet with parchment paper or use a nonstick baking sheet.

In a medium bowl add ⅔ cup hazelnut butter, ½ cup granulated sweetener (90 g), ¼ cup cacao powder (22 g), 1 large egg, a pinch of sea salt, and the optional ½ teaspoon vanilla extract if using.

Mix the ingredients with a fork until the mixture is smooth and uniformly combined, scraping the sides of the bowl as needed.

Portion the dough into small balls of about 15 g each (or use a small cookie scoop).

Place the balls on the prepared baking sheet, leaving a little space between each cookie.

Flatten the tops of the cookies with a fork to create a criss-cross pattern. Smooth the edges with your fingers if desired to reduce cracking.

Bake for about 8 minutes, until the edges are set and firm. Avoid overbaking — the cookies will continue to firm up as they cool.

Remove from the oven, transfer the cookies to a wire rack or leave on the baking sheet, and let them cool completely before eating. They will be soft hot out of the oven and become crisp once cooled.