Put an empty 9½-inch glass pie dish into a cold oven and preheat the oven to 350°F [175°C].
Make the Caramel
DO NOT RUSH the caramel-making process. It is not a difficult process, but it does require some patience. This step should take about 25-30 minutes. In a small stainless saucepan, heat the sugar over MEDIUM-LOW to LOW heat.
Shake the pan occasionally to distribute sugar evenly. As the sugar begins to melt, stir occasionally with a wooden spoon, but don’t overdo it or the sugar will crystalize and clump too much. Scrap down crystals that form on the sides of the pan as much as possible.
Continue to melt and brown the sugar until it liquifies. The caramel is ready when it is thin, translucent, and dark amber in color.
Pour the Caramel
Remove the hot pie dish from the oven and immediately pour in the caramelized sugar, swirling to coat the bottom of the pan evenly. Set aside.
Make the Custard
In a blender, combine sweetened condensed milk, cream, milk, eggs and vanilla and blend on high for about a minute.(You can also just whisk the custard ingredients together by hand.)Set the custard mix aside until you are ready to pour it into the pie dish.
Prepare the Bain-Marie (Hot Water Bath)
Put a large pan or casserole dish (one big enough for your pie dish to easily sit inside of) into the oven. Set the pie dish with the caramel in the bottom into the larger pan.Carefully pour the blended custard mixture over the caramelized sugar.
Add about 1-inch of very hot water to the outer pan, being careful to avoid getting any water in the custard.
Bake the Flan
Bake the prepared flan in a preheated oven 350°F [175°C] oven for 50-60 minutes. Check for doneness.
The flan is ready to take out of the oven when the center is still slightly wobbly when gently shaken. It should wobble like one unit - like set Jello - however, it should not slosh or ripple. The internal temperature will be 170-175°F [76-79°C]. The flan custard will continue to cook after it is removed from the oven for at least 10 minutes.
Flip the Flan
In a perfect world, refrigerate the baked flan overnight.If you want to serve it today, allow the flan to cool completely on the counter, and then refrigerate for at least 3 hours. If you want to serve it right now, allow it to cool for exactly 10 minutes; no more, no less. (The 10-minute method is only recommended if you are (a) in a real hurry to get the flan on the table, and (b) confident in your flan-flipping skills. You will need to use a pot-holder to hold the hot flan pan if you proceed this way.) When you are ready to flip the flan: Run a sharp knife around the edge of the pie dish.Place a large rimmed serving plate on top of the flan in the pie dish. Carefully and quickly, flip the flan over. Gently tap the side of the dish to encourage the flan to release. Carefully lift the pie dish off the flan.Allow to cool completely, and then refrigerate until ready to serve.
Serve the Flan
Flan is traditionally served cold, after everything has had a chance to firm up. To serve, cut into wedges or spoon onto dessert plates.
To avert burns, use silicone potholders or gloves to lift the pie dish up and out of the hot water bath. to avert burns. Avoid using cloth potholders, as they get wet too easily and then become heat conductors.