In a bowl, combine almond flour, sugar, butter, egg yolk, and almond extract. Mix until smooth and well combined.

Scoop into 16 portions and place on a parchment paper-lined baking sheet. Chill the filling in the refrigerator for at least 30 minutes or the freezer for 20 minutes. This step firms up the filling, making it easier to handle and shape.

In a mixing bowl, cream the butter, brown sugar, and sugar until light and fluffy about 3-4 minutes. Beat in the egg, egg yolk, and almond extract.

Gradually mix in flour, baking soda, and salt until a soft dough forms.

Preheat your oven to 350 degrees. and line baking sheets with parchment paper. Roll the dough into 16 balls. Flatten each ball into a disc and place a chilled almond filling portion in the center of each cookie.

Fold the edges of the dough over the filling, pinching and sealing the edges completely. Gently roll the dough into a ball to ensure the filling is fully encased. Press sliced almonds on the top of each cookie dough ball. If you want a slightly flatter cookie, press down on the ball with the palm of your hand to slightly flatten it.

Arrange the cookies on the prepared baking sheets, spacing them about 2 inches apart. Bake for 10-13 minutes or until the edges are lightly golden.

Cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely. Once cooled, dust with powdered sugar.