Add in the egg yolks, then the flour to form a dough. Wrap dough in cling film and place in fridge for 1 hour.
Preheat the oven to 160 C / Gas 2 1/2.
Roll dough in between 2 sheets of wax paper. Cut out 12 pieces 4cmx14cm.
Bake these biscuits for 15 minutes.
For the caramel, put the condensed milk tin in a pot. Cover with water and boil for 2 hours, making sure that the tin remains covered with water, then cool for 30 minutes.