In a bowl, aggressively whisk together the almond flour, coconut flour, baking powder, and sea salt to aerate the mixture.
In a stand mixer, cream the softened butter and your chosen sugar substitute on medium-high for exactly four minutes until light and fluffy.
Reduce speed to low, add the room-temperature egg and vanilla extract, and mix just until incorporated.
Gently fold the dry ingredient blend into the wet mixture until a cohesive dough forms.
Wrap the dough tightly in plastic wrap and chill in the refrigerator for a minimum of 2 hours.
Preheat oven to 325°F (165°C). Roll the chilled dough between parchment paper to 1/4-inch thickness and cut into shapes.
Bake for 10-12 minutes until the edges are golden and set.
Cool on the baking sheet for 10 minutes before transferring to a wire rack to crisp completely.
