In a small saucepan, heat the water and white sugar over medium heat. Don’t stir them to combine but, rather, swirl the pan about until all the grains of sugar are wet. Let this come to a boil, where it should stay for about 5 - 7 minutes, or until it starts to turn a medium-dark brown color. Be very watchful of this – it will seem, for the first several minutes, that it will never turn that caramel color and then in the last minute or so it will start to darken rapidly and you don’t want to burn the sugars.
Once you’re at this stage, drop in the brown sugar and kosher salt, swirl to combine and immediately, but very carefully, pour in the half and half and stir everything to combine. If the tanned sugars harden just keep whisking in the warm cream until they melt back down.
Once the cream mixture is hot take out a small ladleful (maybe 3 – 4 tablespoons-worth) and pour into a small bowl with the cornstarch.
Whisk the cornstarch and cream together into a smooth paste and pour into the caramel-milk once it’s returned to an almost-boil and stir to incorporate it.
Turn the heat down and simmer for just a minute or two until its very thick and the consistency of, well, pudding.
Turn off the heat, whisk in the butter and vanilla and transfer to a small serving bowl. Let it come to room temperature, cover with plastic wrap and give it a few hours to chill and set up in the fridge.
When you’re ready, sprinkle with coarse sea salt and indulge.
- Half and half works best. Heavy cream makes it too thick and milk, even full fat, doesn’t give you the right level of lush