I learned to make this in South America. The recipe (for pudim which is pretty close to the same as flan) was on the condensed milk can. It's easy and, in my family, we love it.
First I hunt up my bundt cake pan and set it next to the stove. Then I turn on the oven to 325 degrees. Then I get another cake pan that the round one will fit in and fill it with about an inch or so of water.
Next, I put a skillet on the stove and throw at least a half cup of sugar into it. Usually more. You can melt the sugar fast with the heat on high, but you have to stand there and watch so it doesn't burn. Or you can melt the sugar more slowly and control how carmelized it gets.
Now I pour the carmelized sugar into the bundt pan and swirl it up on the sides as much as I can. (the caramel sugar will set and be hard --- don't worry -- it will melt in the oven) Set it aside.
Open a can of condensed milk. Empty it into the blender. Fill the can with milk and add that to the blender. Add four eggs. The flan will be smoother, if you add three eggs and one egg yolk. Then add vanilla. I use about half a teaspoon. I actually also add a pinch of a pinch of salt, but not necessary. Blend it. (You can use a mixer, but beat the eggs first thing.)
Now you have thoroughly blended the custard mixture and you can pour it into the cake pan. Place the pan into the pan with water in it. Put the custard in the water bath into the oven and bake it for about 50 minutes. Test for doneness with a clean knife blade.
When it's done and you take it out of the oven. Let it sit four or five minutes. Separate the custard from the pan with a knife. Cover the pan with a large plate and quickly upend the pan so the custard falls onto the plate. (The carmelized sugar will run so allow room.) Let it cool, if you can wait that long.
You don't have to use a bundt or tube pan, but you do have to use the water bath.
I assume nurses know custard has to be refrigerated.
Oh! Please let me know how it turns out, if you decide to give it try.