Preheat oven to 220°C.

Pour the sweetened condensed milk into an oven-proof dish. Sprinkle over sea salt if needed. Tightly cover the dish with foil.

Place covered dish in a roasting pan and fill with water until it comes 3/4 of the way up the oven-proof dish, to create a water bath.

Place in the oven and cook for 1 hour and 30 mins, checking every 30 mins to top up the water bath if need be (I had to top the water up once).

Once the mixture is nicely browned and caramelised, remove from the oven and let it cool down.

Once cool, whisk the dulce de leche until smooth.

Store in an airtight, clean container (I used a mason jar).