Preheat oven to 350°F (175°C). Line a baking sheet with a silicone baking mat or parchment paper.
In a large mixing bowl, beat the softened butter and sugar substitute together on medium speed for 2 minutes until light and fluffy.
Add the egg, lemon zest, and lemon juice. Mix on low for 30 seconds, then increase to medium and beat for 1–2 minutes until the mixture is smooth and fluffy. Scrape down the sides of the bowl as needed.
Add half the almond flour and beat until just combined. Add the remaining almond flour, baking soda, and salt. Mix until a soft dough forms. Do not over-mix.
Scoop about 1½ to 2 tablespoons of dough per cookie and roll into balls. Place on the prepared baking sheet. Gently flatten the tops with your palm or the back of a spoon.
Bake for 8–12 minutes, until the edges are golden and the bottoms are lightly browned. The centers will still look slightly soft - that is correct. Do not overbake.
Remove from oven and let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack. Allow to cool completely before serving.