Faster, more consistent cooking is the hallmark of a cartouche.
In our recipe for Slow-Cooked Whole Carrots (see related content), we found that using a cartouche—a round of parchment paper placed directly on top of food during cooking—was key for cooking the carrots efficiently and evenly. Why not just use a partially covered pan? The cartouche was able to trap steam directly on top of the carrots while still allowing it to escape around the edges of the paper, leaving the carrots perfectly cooked through and with just the light coating of glaze that we wanted. We found that although a partially covered pan traps some steam, the cooking isn’t as even, fast, or consistent.
Here’s why: A metal lid absorbs heat energy more readily than parchment does, so the steam in a lid-covered pot loses much of its energy to the lid and condenses. There is actually less steam cooking the food in a lid-covered pot, and the cooking and evaporation are slowed. Also, because condensation is uneven across the bottom of the lid, some areas are cooler than others, leading to uneven cooking.