In a medium bowl, whisk together melted butter, granulated sugar, and egg yolk until smooth. Mix in vanilla extract, almond extract, ground almonds, all-purpose flour, and salt, set aside.

In another bowl, combine all-purpose flour, baking powder, baking soda, and salt. Stir until evenly mixed and set aside.

Cream room temperature butter with granulated sugar and brown sugar using an electric mixer until light and fluffy (about 2 minutes).

Add egg yolks, vanilla extract, and almond extract to the creamed mixture, mixing until pale and fluffy (1-2 minutes).

Gradually add dry ingredients and remaining ground almonds, mixing on low speed until just combined, careful not to over-mix.

Using a cookie scoop, portion out the dough into 18 equal balls. Place on a baking sheet and indent each ball. Fill each indent with frangipane mixture and sprinkle with sliced almonds.

Preheat oven to 350°F (175°C). Bake cookies for 12-13.5 minutes or until edges are light golden brown.

Use a cookie cutter to shape each cookie while warm. Allow to cool for 5 minutes before transferring to wire racks. Dust with powdered sugar before serving.