Put 2 cups couscous and 3 cups water in a medium saucepan. Add a large pinch of salt and bring to a boil. Take the couscous off the heat and cover tightly.
Trim and slice the leeks (use only the white and light green part of the stem.) Saute in 3T butter, sprinking with salt and pepper to bring out the flavor. Do not fuly carmelize, but saute them until they're soft, about 6-8 min.
Put the leeks in the bottom of a large oven-proof pan. (I used our largest Pyrex.) Fluff the couscous and layer it on the onions. Top with cheese.
Broil until the cheese is bubbly, about 2-3 min. Let cool briefly before serving.
I used pepper jack and liked the taste, but found it formed a firm crust rather than melting into the couscous. Would Gruyere blend better? Mabye. I may also have broiled it a touch too long.
This made a LOT. I think in the future I'll cut it in half.
The leeks looked huge, but after losing the thick leaves, they were about the size of a medium onion. I was surprised at how much they shrunk while frying, even though they weren't carmelized.