Prepare Frangipane: In a small bowl, whisk together the melted unsalted butter, granulated sugar, egg yolk, vanilla extract, and almond extract until well combined and smooth. Then fold in the ground almonds, all-purpose flour, and a pinch of salt.

Mix Dry Ingredients: In a separate large bowl, whisk together the all-purpose flour, baking powder, baking soda, and remaining salt.

Cream Butter and Sugars: In another large bowl, beat the softened unsalted butter, light brown sugar, and granulated sugar on medium speed until fluffy and pale, about 3-4 minutes. Add the egg yolks along with more vanilla and almond extracts.

Combine Mixtures: Gradually add the dry ingredient mixture to the creamed butter mixture, mixing on low speed until just incorporated. Fold in the reserved ground almonds.

Shape Cookies: Portion the dough into 18 equal pieces, rolling each into a ball. Place them on a lined baking sheet, make an indent in the center of each ball, fill with frangipane, and top with sliced almonds.

Bake: Preheat oven to 350°F (175°C) and bake cookies for 12-13.5 minutes until lightly golden. Reshape with a cutter while warm.

Cool and Serve: Allow to cool on baking sheet for 5 minutes, then transfer to a wire rack. Dust with powdered sugar before serving.