Pre heat the oven to 150oC fan.
Put a 20 x 20cm solid baking dish (or similar) into a large higher sided roasting tray. The flan is baked in a bain maire or water bath set up, so the baking dish for the flan must be smaller than the roasting tray. Place both in the oven to get warm.
To make the caramel, put the sugar in a large sauce pan over medium heat. Do not sir but allow to melt and get brown, swirling the pan to incorporate all the grains of sugar. How dark you take your caramel is a personal preference, we like to take it pretty dark, when it just starts to make your nostrils tingle. Then pour it carefully into your warmed baking dish, tilting the dish to spread the caramel over the bottom. Allow to cool until hard.
Meanwhile make the custard. Squeeze the Chile Ancho of liquid and put into a blender with the other custard ingredients. Blend until smooth.
When the caramel is hard, sieve the custard mix over the caramel. Place the baking dish to the roasting tray and place in the oven. Pour boiling hot water in the roasting tray until half way up the baking dish. Bake for 40-50 minutes until the edges are set, but it is still wobbly in the middle - it will continue to firm up in the fridge.
Once cooked, remove from the water bath and allow to cool. Then cover and refrigerate until for 3 hours or over night.
To release the flan, run a knife around the edge and place a dish that is larger than the baking dish on top, then invert and the flan should release itself, remove the dish and the caramel should be on the top and running don the side to make a glorious puddle. Serve in bowls.