Creme Brulee made with dulce de leche
Rick Bayless has a recipe for flan using sweetened condensed milk that might be a good starting point. He suggests one 14 ounce can, 2 1/4 cups milk, 6 eggs, 6 egg yolks and a tsp of vanilla extract. You might need to add some sugar, depending on how sweet your ddl is, but the big question is how to adjust the ratio of eggs to yolks. For me creme brulee is made with yolks only (up to 3 for every cup of dairy), so if you want to use yolks only, that would be about 12.
I'd start with a small batch (unless you have a big family) to experiment. So if you think in terms of 2:1 dairy to egg by volume, you could use 4 oz of dairy to 1 egg (2 oz in Cda/US).
While I agree with Zeldog about using some yolks only in regular creme brule, I'd start off with whole egg as a starting point. So you could mix 1 egg, 2 oz ddl, 2 oz cream, vanilla, a pinch of salt maybe ? (b/c of the sweetness of the ddl?) . . . pour it into 2 ramekins, bake in a water bath, low and slow. It may not be perfect the first time, but it'll be edible - good even - and you've only used 1 egg and 2 oz of your ddl. If it's too firm you'll know next time to use 2 yolks instead of the whole egg.
Using sweetened condensed milk (or evaporated) in custard is easy enough, but DDL might be trickier. For one thing it it is quite a bit stiffer. You could of course warm it to make it more liquid, but then you'd have problems adding the eggs.
I wonder if they warmed DDL, then diluted it with milk or sweetened condensed, and when it is cool enough added the eggs and such. In effect, a dulce flavored custard, as opposed to one where dulce is the main milk component.