For the Dulce de Leche filling
Heat oven to 425 degrees and placing a rack in the middle of the oven
Pour milk into a glass pie plate and sprinkle with salt.
Cover tightly with aluminum foil and place in a roasting pan with hot water to reach halfway up the sides of the pie plate.
Bake for 1 hour
Remove the roasting pan from the oven and remove the pie plate
Uncover the pie plate, taking care not to burn yourself and whisk the mixture until smooth
Replace the foil, return the pie plate to the roasting pan and add hot water as necessary to remain halfway up the side of the plate.
Put back in the oven.
Continue to bake for about another 1½ hours until the color becomes a caramel color.
Remove from over, let cool, remove the foil and whisk again until smooth.
Set aside for the cookies.
Keep extra in the refrigerator of up to one week.
For the Cookies:
In a medium bowl, whisk together the cornstarch, flour, baking powder, baking soda and salt.
In a separate bowl, using a mixer on medium mix together the butter and sugar until it is light and fluffy. Add in the egg yolks one at a time, the brandy, and vanilla.
Start slowly adding in the flour mixture until incorporated, taking care not to over mix.
Turn the dough onto a piece of plastic wrap and shape into a smooth disk, wrap it tightly and let sit for one hour in the refrigerator.
Preheat the oven to 350 degrees
Line two cooking sheets with parchment paper
Remove the dough from the refrigerator and lightly flour your work surface.
Lightly flour the top of the dough
Roll out to ¼ inch thick, do not be considered if it cracks, you can easily patch it together.
Stamp out 24 rounds using a plain or fluted 2” round cutter, reroll the dough as necessary.
Place 12 cookies ½ inch apart on each prepared cookie sheet and bake 1 sheet at a time on the middle rack.
Bake for 12-14 minutes (Cook until just firm and slightly golden on the bottom, the top will remain light.)
Transfer to a wire cooling rack
Once completely cool, flip half the cookies upside down and gently spread with about 2 teaspoons of Dulce de Leche. Place another cookie on top to make a sandwich.
Sprinkle with powdered sugar before serving.