Preheat oven to 320F or 160C
In a bowl, whisk the butter and powdered sweetener until pale in color.
Add the egg yolk, vanilla extract and whisk to combine.
Add the ground almond, salt and mix with a spatula until a dough is formed.
Shape the dough into a ball.
Portion the dough into 15 g each then shape into balls and place on a baking tray lined with parchment paper. The dough will not spread much during baking so you do not have to leave a huge gap in between. This recipe makes about 21 cookies at 15 g per each.
Make an indentation with your thumb or the back of a small measuring spoon. If you shape the dough and make the indentation quickly, you will get a nice and smoother texture. If you leave the dough exposed to air longer, you will get cracks when you make the indentation.
Fill with the jam. The jam will not overflow during baking.
Bake at 320F or 160C for about 12 to 15 minutes depending whether you prefer a softer or crispier texture.
Cool for about 5 minutes then transfer the cookies to a wire rack to cool completely. The cookies will firm up once cooled.
Store in an airtight container. These cookies can be kept at room temperature for up to a week provided you have a cool and dry climate. Otherwise, it's better to refrigerate earlier as the cookies are soft and moist. They are firmer and crispier when chilled and tastes great. They can also be frozen.
The dough can be frozen and baked at any time.