Preheat the oven to 350°F and line a baking sheet with parchment paper or a silicone baking mat.

In a medium mixing bowl, beat the softened butter and sugar substitute together with a hand mixer until pale and fluffy, about 2 minutes.

Add the egg and beat until fully combined, scraping down the sides of the bowl as needed.

Mix in the lemon juice and lemon zest until the mixture looks mostly smooth and evenly combined.

In a separate bowl, whisk together the almond flour, baking soda, and salt, breaking up any lumps.

Add the dry ingredients to the wet mixture and stir with a spatula just until a soft dough forms and no dry spots remain.

If the dough feels very sticky, chill it in the refrigerator for 10 minutes to firm slightly.

Scoop the dough into 12 equal portions, roll each portion into a ball with your hands, and place them on the prepared baking sheet, spacing evenly.

Lightly flatten the tops of each dough ball with your fingers or the bottom of a glass, shaping them into thick discs.

Bake for 8 minutes, or until the edges are lightly golden and the centers look set but still soft.

Remove the baking sheet from the oven and let the cookies cool on the sheet for 5 minutes to firm up.

Transfer the cookies to a wire rack to cool completely before serving or storing.