Make the Blueberry Filling:

1. In a small saucepan over medium heat, combine blueberries, sugar, and lemon juice. Cook until blueberries soften and release their juices (about 3–5 minutes).
2. In a small bowl, mix cornstarch with 1 teaspoon of water to make a slurry. Stir into the blueberry mixture and cook until thickened (about 1 minute).
3. Remove from heat and let cool completely.

Make the Cookie Dough:

4. In a large bowl, beat butter and powdered sugar until light and fluffy.
5. Mix in vanilla and almond extracts.
6. Add flour, salt, and ground almonds, mixing until a soft dough forms.
7. Wrap dough in plastic wrap and chill for at least 30 minutes.

Assemble the Cookies:

8. Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
9. Scoop about 1 tablespoon of dough, flatten it in your palm, and place a small spoonful of blueberry filling in the center. Carefully wrap the dough around the filling and roll it into a ball.
10. Place cookies on the baking sheet, spacing them about an inch apart.

Bake & Coat:

11. Bake for 12–15 minutes, until the bottoms are lightly golden. Let cool for 5 minutes.
12. Roll warm cookies in powdered sugar, then let them cool completely before rolling them in powdered sugar again for a snowy effect.