In a small bowl, whisk together the melted butter, sugar, egg yolk, vanilla extract and almond extract until well combined.

Fold in the ground almonds, flour and a pinch of salt. Cover the bowl and set aside.

Before starting on the dough, preheat the oven to 350℉. Position the baking rack in the center of the oven. Line two large baking sheets with parchment paper.

In a medium bowl, add the flour, baking powder, baking soda and salt. Whisk until well integrated. Set the flour mixture aside.

In a large bowl, cream the butter, brown sugar and granulated sugar together with an electric mixer on high speed until fluffy for about 2 minutes. A stand mixer or hand-held mixer can be used.

Add the egg yolks, vanilla extract and almond extract. Mix on medium speed until fluffy and pale in color. 

Add the flour mixture and the ground almonds to the wet ingredients. Mix on low speed until just combined.

Scoop the cookie dough with a 1.5 tablespoon capacity cookie scoop into 24 portions. If you slightly overfull the scoop, you should end up with 24 rounds of dough.

Roll each into a ball and use the bottom of a rounded 1/2 tablespoon measurer to make a slight indent in each round of dough. Add a level 1/2 tablespoon of frangipane to the center of each dough ball and slightly flatten it out. Top with the sliced almonds.

Arrange the cookies on the large prepared baking sheets, with space in between to allow for spreading. Bake one sheet at a time, for 12 to 13 minutes until they are a light golden brown.

When the cookies are straight out of the oven, scoot a large circular cookie cutter around each one to give them a perfect circular shape. Since they tend to spread unevenly while they bake, scooting a cookie cutter around them is recommended to get the perfectly round shape and proper thickness.

Allow the cookies to cool on the cookie sheet for a full five minutes before transferring them to a wire rack to completely cool. Once cooled, dust each cookie with the desired amount of powdered sugar.