In a medium bowl, whisk together 3 tablespoons of melted unsalted butter, 1/3 cup granulated sugar, and 1 egg yolk. Add 1/2 teaspoon of vanilla extract and 1/2 teaspoon of almond extract, stirring until smooth. Carefully fold in 1/4 cup plus 2 tablespoons of ground almonds, 1/3 cup of all-purpose flour, and 1/2 teaspoon of salt. Set the frangipane aside.

In another bowl, sift together 1 3/4 cups of all-purpose flour, 1/2 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt. Set aside.

In a large mixing bowl, cream together 3/4 cup of brown sugar and 1/3 cup of granulated sugar with 1/2 cup of softened unsalted butter for about 2 minutes until light and fluffy.

Slowly mix in the reserved egg yolk, 1/2 teaspoon of vanilla extract, and 1/2 teaspoon of almond extract. Beat until well combined.

Gradually incorporate the dry ingredients into the creamed mixture, mixing gently until just combined. Fold in the remaining 1/4 cup of ground almonds.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop the dough into 18 equal portions, rolling them into balls. Make a slight indent and spoon the frangipane filling into the center. Top with sliced almonds.

Place the cookies on the baking sheets about 2 inches apart. Bake for 12-13.5 minutes until edges are golden and centers are set but soft.

Allow the cookies to cool on baking sheets for 5 minutes, then transfer to a wire rack. Lightly dust with powdered sugar before serving.