Preheat oven to 375 degrees. Line a large baking sheet with parchment paper. Sift the dry ingredients into a large mixing bowl until combined and there are no lumps. Set aside. In a large mixer bowl, beat the softened butter and both sweeteners together on medium speed for 1 minute until smooth.
Scrape down the sides of the bowl. Add the eggs and vanilla. Beat until fully combined. Gradually stir the dry ingredients into the wet ingredients until a smooth dough forms. Scoop dough out 1 TBS at a time onto prepared baking sheet. Roll each scoop into a smooth ball
Use hands and flatten each dough ball into a flat disc about 1 1/2 inches in diameter. Leave space between each cookie. Bake the cookies in the preheated oven for 8 to 10 minutes or until slightly darkened on edges. Once baked, remove the cookies from the oven and allow to cool on the pan 7 to 10 minutes until form. transfer cookies to a wire rack and cool completely before assembling
Filling
Combine all the filling ingredients except the powdered sweetener in a large mixer bowl. Beat on medium 1 minutes until smooth. Scrape down the sides of the bowl. Gradually beat the sweetener in until fully combined and smooth. If needed add up to 1 TBS keto milk of choice. The filling should be firm but able to spread.
Assemble
Turn half of the cookies upside down on a clean worksurface. Spoon the filling out 1 TBS at a time in the center of the upside-down cookies. Use a butter knife and smooth the top of the filling. Place a plain cookie on top of the filling. Gently press the cookies together until the filling covers the entire cookie.