Cookies
Preheat the oven to 325°F and line two baking sheets with silicone mats. You can use parchment instead but keep a close eye on your cookies as the bottoms may brown quickly.
In a large bowl, beat the butter with the sweetener until light and fluffy, about 2 to 3 minutes. Beat in the egg, egg white, and vanilla until well combined.
Add the almond flour and salt and beat until the mixture is uniform, scraping down the sides of the bowl and the beaters as necessary.
Cut a 1 inch diameter hole in a piping bag and fill with the dough. Pipe 2 inch long logs onto the prepared baking sheets, leaving at least 2 inches between each cookie.
Bake 18 to 25 minutes, until the edges are golden brown, and turn the oven off. Remove and let cool 15 minutes, then return to the still warm oven for another 15 to 20 minutes, keeping your eye on them, to help them crisp up.
Let cool completely before filling.
Chocolate Mint Filling
In a small saucepan over medium low heat, bring the cream to just a simmer. Remove from heat and add the chopped chocolate. Let sit 5 minutes to melt.
Add the mint extract and whisk until smooth and thick. Spread the bottom of one cookie with about 1 teaspoon of the chocolate filling. Top with another cookie. Place on a cooling rack until firm.