1 can of sweetened condensed milk
A pot of boiling water
You'll want to make Dulce de Leche the night before you make anything that uses this.
All you need to do is take a can of condensed milk and puncture 2 holes on each side of its top.
Fill a pot with enough water to submerge the can, leaving it about half an inch above the water
Boil the can for 2 hours. You will need to refill the water one or two times as it evaporates. Also make sure to remove the label so it doesn't flake off in the pot.
The result should be a thick carmel. Let cool overnight in the fridge.