01 - Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
02 - Whisk blanched almond flour, erythritol, baking soda, and sea salt together in a large bowl.
03 - Incorporate melted butter, egg, and vanilla extract into the dry mixture until a uniform dough forms.
04 - Gently fold toasted sliced almonds into the dough to distribute evenly.
05 - Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing evenly; flatten each slightly with fingers or a fork.
06 - Bake for 12 to 15 minutes, or until cookie edges turn golden brown; allow cookies to cool completely on the baking sheet to firm up.
07 - Beat softened butter with powdered erythritol until smooth; add heavy cream, vanilla extract, and a pinch of salt, then continue beating until creamy and fluffy.
08 - Once cookies are fully cooled, spread or pipe frosting atop each cookie; optionally garnish with additional toasted almonds.
09 - Place cookies in an airtight container and refrigerate; they will keep up to 5 days.