Sift all the dry ingredients, then add butter, and integrate with a fork.
add yolk, integrate, add milk just enough to make all the dough to get together.
let the dough rest for 30 min on the fridge. once rested roll your dough about 1/2 inch maybe a bit thinner
With the help of a cookie-cutter shape the dough and put the dough on a tray
Cook it on your oven at 350 F or 180 C for 10 minutes
Once it's cooked, put some dulce de leche on one side of a cookie and cover with another cookie to get a sandwich then finish with some caster sugar on top