"Bain Marie" means water bath, also nicknamed double boiler. What is it? You can buy a double boiler pan. It is two pans stacked on top on one another. The bottom of the pan is filled with water and the top pan is filled with the food to be "cooked" by the heat and steam.
You can also improvise a bain marie. How? Simmer a pan of water and place a stainless steel bowl over the pan. Fill the bowl with the food that is about to be cooked. Which is better: to buy a tradition bain marie or improvise? Improvise. Yes, I have a traditional bain marie stainless steel clad construction pot that my grandmother gave me. But I almost always improvise. Why? Most people have a stainless steel bowl and pan in their kitchen. Don't waste more money on ANOTHER pan you have to put in your kitchen.
How to make your own person bain marie:
1) In a medium size sauce pan (about 3-4 quarts), fill half way with water.
2) Put it on medium-high heat. Let boil. Turn heat down to medium, thus the water is at a simmer.
3)Put your ingredients in a stainless steel (NOT plastic or glass! Stainless steel can take high heat VERY WELL!). Place the bowl over the pot of simmer water. Using your kitchen utensils, stir until cooked/thickened. (You may choose to wear an oven mit during this process, the steam is very hot!)
4) Remove bowl, be careful of the steam. Turn off the stove top.
Why a bain marie? It "cooks" food gently and softly. It is meant for food that, when exposed to direct heat, will scorch or burn.
A bain marie is keeps food nice and hot! Think: those fancy chauffer dishes for buffet dinners.
Most popular foods that need to be cooked in a bain marie:
-Custards, like creme brulee
-Hollindaise sauce, for eggs benedict
-Warm milk, like for baby's forumla
-Charcuterie items, like pate and terrines
Most people do not use a bain marie ENOUGH to buy a tradition bain marie. Just improvise and get cooking! Remember, the steam that is released is very hot and dangerous. I like wearing an oven mit when I am cooking food over a bain marie.