Preheat your oven to 350°F (175°C) and get a baking sheet ready by lining it with parchment paper.
Combine the cold butter, almond flour, coconut flour, sweetener, gelatin, and vanilla in a food processor. Pulse and blend until you have a smooth, uniform cookie dough. This might take 2-3 minutes on high speed.
Use a medium cookie scoop to form 10 cookies, placing them on your prepared baking sheet. Gently press down on the center of each cookie with your thumb or a teaspoon to make a little indentation.
Bake the cookies for 12-15 minutes, or until their edges turn a light golden brown. Let them cool on the baking sheet for at least 10 minutes.
While the cookies are cooling, it's time to melt the chocolate. Place the dark chocolate squares in a microwave-safe bowl. Heat for 30 seconds, then stir. Repeat this heating and stirring process until the chocolate is completely melted and smooth.
Spoon 1 teaspoon of the sugar-free chocolate hazelnut spread into the well of each cooled cookie, spreading it evenly.
Finally, carefully drizzle the melted dark chocolate over each cookie. Store them in a single layer in an airtight container.