Preheat the oven to 300°F. Line a cookie sheet with parchment paper.
Make the cookies: In a large bowl, whisk together the almond flour, chocolate collagen, sweetener, baking powder, and salt. Add the melted butter, egg, and vanilla and stir well to combine into a thick dough.
Roll out the dough on a large piece of parchment until it is ¼ inch thick. Use a round cookie cutter that is 1½ inches in diameter to cut out the cookie shapes. You will get about 50 cookies. Place the cookies on the prepared cookie sheet.
Bake for 18 to 20 minutes, until the edges are lightly browned. Turn off the oven and leave the cookies in the oven for 15 more minutes to crisp up. Remove and allow to cool completely.
While the cookies are cooling, make the filling: Put the butter and cream cheese, in a medium bowl and use a hand mixer to mix well. Stir in the sweetener, salt, and extract or spice, if using. Taste and adjust the sweetness to your liking.
Once the cookies are cool, pipe or spread a tablespoon of the filling on a cookie. Top the filling with another cookie to make a sandwich. Repeat with the remaining cookies and filling.
Store extras in an airtight container in the refrigerator for up to 5 days.