This is a culinary term which means to bake something - usually meat or fish with aromatic herbs and sometimes vegetables as well - wrapped in parchment paper or tin foil. (Fruit is sometimes used as well, to make a dessert.) The name comes from the French word for butterfly, papillon, presumably meant to refer to the shape the paper is cut into, though actually, it's more like a heart.
Tender and delicate foods like fish fillets are ideally suited to being cooked en papillote because they cook rather quickly and benefit from the moisture trapped inside the paper (or foil) package. If you're using firmer vegetables like potatoes, carrots, and the like, you'll want to blanch them first so that they'll cook in the same time as the fish. Or you can use chicken or veal instead of fish.
Here's a suggestion:
- Slice a medium potato thinly, blanch it for 2 minutes, and drain well.
- Cut out 2 X 15 inch parchment paper hearts, and put half the potatoes in the middle of one side of each heart. (If you don't have parchment paper, use tin foil. It won't puff up as nicely, though.)
- Place a piece of salmon fillet, skinned, on top of the potato.
- Sprinkle the fish with a little garlic, lemon zest, salt, pepper, and thyme (or anything else you think might be good: olives and caramelized onions spring immediately to mind), and drizzle with olive oil.
- Fold the other half of the heart over the top of all this and, starting from the top, begin rolling the edges of the paper together to form a tight seal. (If you're having trouble picturing this, go to www.reynoldskitchens.com/ReynoldsKitchens/kitchenconnection/products/parchment_paper and follow the link to papillote for visual cues.)
- Place the packages on a cookie sheet and bake in a 400° F oven for 20 minutes. The paper should be browned slightly and the packages should have puffed up with steam.
- To serve, slide the packages onto 2 plates, set in front of your companion and yourself, and use a sharp knife to puncture the paper, releasing a waft of delicious aromatic vapour. Set to!