Cornstarch sandwich cookies filled with dulce de leche

I love these cookies and I sincerely believe that this recipe is perfect, I have done it many times and the cookies have a delicate texture that melts in your mouth, not too sweet to complement the dulce de leche and the crunch of the nuts, mhmmm
This recipe is adapted from our family recipe. These cookies keep their shape very well, so others can try cutting them with simple molds.
You can find this cookies in Chile, Peru and Argentina, most people think they were "born" in Peru, probably in a convent and from there when to Chile and Argentina.
 
Cornstarch sandwich cookies filled with dulce de leche
Approximately 35 sandwich
Ingredients:
for the cookies,

• 225 grams/ 8 oz unsalted butter at room temperature
• 1 cup powdered sugar
• 4 egg yolks at room temperature
• 1 teaspoon vanilla extract
• 2 1/2 cup cornstarch
• 1 1/2 cup plain all purpose flour 

to assemble the cookies,

• Powdered sugar for dusting
• Chopped or ground walnuts to cover the edge
• Dulce de leche to fill, I use La Lechera brand sell in a can on Latin markets

Directions:

1. Working with stand mixer with the paddle attachment. Beat softened the butter with the sugar until a creamy white and fluffy, about 3 minutes, add the yolks one at a time, beating to incorporated completely, about 2 minutes. Add the vanilla and mix well. Add all the flour and cornstarch and beat until crumbs are formed, continue working with your hands to form a soft dough. Wrap it with plastic and refrigerate at least 30 minutes or leave the whole night.
2. Preheat oven to 350F or 180C.
3. Divide dough into 2 equal portions. Take one half and rolled over a silpat or a floured counter until it's 1/2 cm or 1/4" thickness, not less because they are very fragile. Cut circles with a cookie cutter (I use a 2 cm/1" diameter) and bake on a baking sheet over silicone paper or Silpat in preheated oven for 13-15 minutes until lightly browned underneath. They can be close together as almost do not grow.
4. Cool completely. Filled with the dulce de leche and also apply a thin layer around the edge, then roll the edges on the ground nuts. Finally sprinkle through a sieve with powdered sugar.
5. Let stand 2 hours before serving, also can be assembled the day before. They last well 3 days in a air tight box at room temperature.