Syrup
To make the syrup, add the sugar, the water and the vinegar into a pan, stir gently, stop stirring and let it simmer into a caramel syrup.
The longer it stays over heat, the darker it gets.
Grease a ring mold with this caramel syrup while still hot and using a spatula, spread it all around the edges of the mold. Set aside.
In a blender, blend the condensed milk and the plain yogurts for 4 minutes.
Pour it into the mold, passing it through a sieve.
Heat some water in a pan and put the mold in it. Take it to the oven, in a double boiler.
Bake in a preheated oven at 180°C (356°F) for 45 minutes.
Let it cool down and chill in the fridge for 1 hour.