Add flour, cornstarch and salt to a medium bowl, and whisk to combine. Set aside. Combine butter, granulated sugar in the bowl of a stand mixer fitted. Cream the butter mixture on medium-high speed until light and fluffy, 2 to 3 minutes. Add vanilla medium speed until well combined. Add the flour mixture to the butter mixture and beat on low speed just until combined.

Scrape the bowl and fold a few times to make sure everything is well combined.

Wrap dough in plastic wrap, flatten into a disk, and chill until firm, at least 1 hour.

Cut dough into 8 pieces. Take one piece out and return the rest to the refrigerator.

Take each piece into a ball between your hands. One at a time, dip a ball of dough into flour and set on the work surface. Roll out into a circular shape.

Set the balls aside so you can use them for the center.

Take the dough in one hand and place the brownie ball in the center. Cover the brownie by pinching the dough in one direction until a ball has been formed.

Dip cookie stamp in flour, remove and press down on the ball of dough until it is about 1-inch thick. Remove stamps. Transfer mooncake to a parchment baking sheet, arranging them about 1 ½ inches apart. Repeat with remaining dough.

Once you have stamped out all the cookies, chill in the freezer until very firm, about 10 minutes. Set the oven at 350 º degrees.

When cold, brush off any excess flour with a dry pastry brush.

Remove the mooncakes and cool for a few minutes on a wire rack. EnJoY!