Mix the almond flour, granulated sugar, egg white, and almond extract until a thick paste forms. Divide the filling into 12 portions and refrigerate for 20 minutes.
Preheat the oven to 350 F and line two baking sheets with parchment paper.
Beat the butter and granulated sugar until light and creamy. Mix in the whole egg, egg yolk, and vanilla until smooth.
Add the flour, baking powder, and salt to the butter mixture. Mix just until a soft, pliable dough forms.
Divide the dough into 12 portions and flatten each one. Place an almond filling portion in the center, enclose it completely with dough, and gently flatten the filled cookie.
Press sliced almonds onto the tops and arrange the cookies on the prepared baking sheets. Bake for 13 to 15 minutes, until the edges are lightly golden.
Cool the cookies for 10 minutes before transferring them to a cooling rack. Dust with powdered sugar once completely cool.