In a large bowl, add the butter and erythritol sweetener. With an electric mixer, beat the mixture for 2 to 3 minutes, until fluffy. Add the egg, egg white, vanilla, and orange zest, and whisk well. Beat in the almond flour, xanthan gum, and sea salt, at low speed.

The dough will be sticky. Cover and refrigerate for at least 2 hours or overnight.

Preheat the oven to 350ºF. Line two baking sheets with parchment paper.

Remove the dough from the refrigerator and let it sit at room temperature for about 10 minutes. Place the dough between 2 sheets of parchment paper. With a rolling pin, roll the dough about ⅛ to ¼ inch thick. With a 2-inch oval or round cookie cutter, cut the cookies.

Transfer the cookies to the prepared baking sheet. Bake for 9 to 10 minutes, until the cookies are slightly brown around the edges. Allow the cookies to cool for 5 minutes on the baking sheet. Transfer the cookies to a wire rack to cool completely

In the top of a double boiler, melt the dark chocolate. Transfer the melted chocolate to a bowl.

Add the heavy cream and orange extract and whisk until combined.

Spread the filling over 1 cookie. Top with another cookie to make a cookie sandwich. Repeat with all the remaining cookies and filling. Let sit for the filling to cool completely before serving.