Combine almond flour, hazelnut flour, coconut flour, and salt in a bowl and set aside. In a separate bowl, beat the softened butter with granular Swerve sweetener until light and creamy, about 2-3 minutes. This creaming step incorporates air into the dough, giving the cookies a better texture. Add the egg and vanilla extract, beating until fully incorporated. Gradually add the dry flour mixture, beating until a cohesive dough forms. The dough should hold together but not be sticky.

Dust your work surface lightly with coconut flour to prevent sticking. Roll out the dough to an even 1/4-inch thickness. Using a 2 1/2-inch round cutter, cut out as many cookies as possible from the dough. From half of these cookies, use a 1-inch cutter to cut out center windows—these will be your top cookies. Gather and re-roll any scraps, repeating the cutting process until all dough is used. Arrange all cut cookies on parchment-lined baking sheets and refrigerate for 1 hour. This chilling step prevents the delicate almond-based dough from spreading excessively during baking.

Preheat your oven to 325°F. Remove the chilled cookies from the refrigerator and bake for 15-20 minutes, until they are light golden brown around the edges. Keep a close eye on them toward the end of baking, as almond-based cookies can brown quickly. Let the baked cookies cool completely on the baking sheet before handling—they'll firm up as they cool.

While the cookies bake, combine fresh or thawed raspberries with water in a small saucepan. Bring to a boil over medium-high heat, then reduce to medium and simmer for 3-5 minutes, stirring occasionally, until the berries break down and the mixture becomes sauce-like. Remove from heat and stir in the powdered Swerve sweetener until fully dissolved. Whisk in the unflavored gelatin, stirring for about 1 minute until smooth and no lumps remain. I find gelatin works beautifully here because it helps the filling set without adding eggs or dairy, keeping the cookies truly keto-friendly. Let the filling cool for about 20 minutes at room temperature until it thickens to a spreadable consistency.

Once both the cookies and filling are cooled, you're ready to assemble. Dust the top cookies (those with the cutout windows) generously with additional powdered sweetener for a classic linzer finish. Spoon about 2 teaspoons of the thickened raspberry filling onto the flat side of each bottom cookie. Carefully press a top cookie onto the filling, window-side up, so the red filling peeks through the cutout. The powdered sweetener on top will create a beautiful contrast with the ruby-red filling visible through the window.