If cartouche makes you think of hieroglyphs then bravo, you're very smart. But hold onto your headress. A cartouche used in a kitchen is a moisture and heat control device in the form of a flimsy piece of parchment paper. In other words, a cooking cartouche is a lot more complicated than pharaonic ruins.
I only use a cartouche for one thing anymore- poaching pears (tho have used it for stews and tomatoes). It's an absolute necessity in this preparation. First, pears are delicate (especially nice ripe ones). When you poach them you want them to infuse in the cooking liquid (in this case I was poaching 8-10 very small pears in one cup water, 1/3 cup sugar, 1/2 vanilla bean, three or four cardamom pods, one cinnamon stick and the zest of one orange). If I simply used a standard pot cover the heat inside the pot would've gotten too high; the pears would have cooked too quickly and not held as much flavor. On the other hand, had I left them uncovered, too much moisture would have been lost AND the pears exposed to air (they're not completely covered in the poaching liquid) would have become discolored and ugly.
So now you just need to know HOW TO MAKE a cartouche so you can enjoy Vanilla Poached Pears.
You will need a circle of parchment paper roughly the same size as your pot. This is made most easily by starting with a large square of parchment and folding it in half diagonally. (Click here to read David Lebovitz's Guide to Pear Poaching.) Place your finger in the center of the long side (which would mark the center of the square were it unfolded) and fold the triangle in half again, keeping a note of that spot where the center of the square would be. Fold a few more times until you have a thin pointy piece of folded paper. Then, hold the paper over your pot with that center point in the center of your pot (you're just marking the radius of the pot). Using scissors trim off the excess parchment (the part that extends beyond the sides of the pot). Now you can unfold all that paper - it should be a nice circle - and use it as a lid. It doesn't have to fit perfectly. See how I just pressed a slightly oversized cartouche onto my pears and up the sides of the pot:
I used ice bath tonite to cool off my tortilla soup in time for dinner. I usually make the soup early in the day but didn't get to it in time today. I like to puree about half the soup - the corn makes it nice and creamy without adding any fat. (And, as predicted, the addition of farmer's market corn was AMAZING!) I don't care to puree all of it because I like to have the soup to have some texture.
To use an ice bath, all you really need are good nesting bowls. I have the stainless steel variety. I wouldn't bother with melamine for a few reasons, not the least of which include possible chemical leach from a hot soup, but also because a stainless steel bowl will, I think, allow its contents to cool faster than a melamine one.
Anyway, fill the bigger bowl with ice, then nestle the smaller one into the ice. Fill the smaller bowl with whatever needs cooling, then stir every so often until the desired temperature is reached. Note: don't go far if you're cooling ganache - left alone for too long and it'll get so hard you'll need to rewarm it and start over. Ganache cools very quickly on ice.