The butter has to be in room temperature. Mix the butter with the sugar powder until mixture is smooth.

Add the egg yolks one by one and mix up till everything looks combined.

In another bowl mix up the flour, Cornflour and backing powder.

Add the dry ingredients to the butter-sugar-eggs mixture slowly and mix till you get a pasty dough.

Put in the refrigerator for 30 minutes. Turn on the oven on 170 C°.

On a clean working table, cut the dough in half and roll out the dough till is 1cm thick.

With a round form or glass, form circles and place carefully on a backing tin. Back for 10-12 min.

After all round cookies are ready, smear some dulce de leche on one cookie and sandwich with another.