Directions

For the dulce de leche: Remove the label from the sweetened condensed milk and place the can on its side in a pot of boiling water. Make sure the water covers the can completely, with at least an inch or more of water above it.
Lower the heat and simmer for 4 hours. Make sure the water covers the top of the can at all times. You will have to pour in more water about every 30 minutes or so.
After 4 hours, remove the can from the water, allow to cool completely, then open the can and stir in salt. Set aside.
For the cookies: Cream the butter and the sugar together until light and fluffy. Add the egg yolks in one at a time, beating until completely incorporated. Add the vanilla extract and mix well.
Scrape down the bowl using a rubber spatula. Add the cornstarch, all purpose flour, baking powder and salt. Beat until a soft dough forms and no streaks of flour remain. Do not overmix.
Turn the dough out of the bowl and shape into two flat oval disks. Wrap tightly in plastic wrap and refrigerate for an hour until firm.
Once the dough is chilled, preheat the to 350ºF and line two cookie sheets with parchment paper. Set aside.
On a well floured surface roll out the dough into a large circle about 1/8 of an inch thick. Use a small round cookie cutter to cut out cookies, placing the shapes on the prepared cookie sheets about an inch apart.
Bake for 8 minutes or until just golden brown on the edges and dry to the touch. Allow cookies to cool completely.
To assemble the cookies take a cookie and spread 1 teaspoon of dulce de leche over the backside. Place a second cookie on top and sandwich together. Repeat with the rest of the cookies. Enjoy!