2 large christophenes
4 tablespoons butter, plus 1 tablespoon butter cut into -inch bits
1Ω cups finely chopped onions
1/3 cup plus 2 tablespoons freshly grated Parmesan cheese
1 teaspoon salt
Freshly ground black pepper
1. Wash the christophenes under cold running water, drain, and cut them lengthwise into halves. Drop into enough lightly salted boiling water to cover them completely and cook briskly for about 30 minutes, or until they are tender and show only slight resistance when pierced with the point of a small, sharp knife.
2. Drain and when they are cool enough to handle, remove and discard the seed and hollow out each half with a small spoon to make boat-like shells about inch thick. Set the shells aside on paper towels to drain completely and chop the scooped-out pulp coarsely.
3. Preheat the oven to 350∞F. In a heavy 10- to 12-inch skillet, melt the 4 tablespoons of butter over moderate heat. When the foam begins to subside, drop in the onions and, stirring frequently, cook for about 5 minutes, until they are soft and transparent but not brown.
4. Watch carefully for any sign of burning and regulate the heat accordingly. Add the chopped squash, 1/3 cup of the cheese, the salt and a few grindings of pepper.
5. Still stirring, cook briskly until most of the liquid in the pan has evaporated and the mixture is thick enough to hold its shape lightly in the spoon.
6. Fill the 4 shells with the onion mixture, patting it in firmly. Arrange the shells side by side in a shallow baking dish large enough to hold them comfortably and dot the tops with the 1tablespoon of butter bits.
7. Sprinkle with the remaining 2 tablespoons of cheese and bake in the middle of the oven for about 20 minutes, or until the tops are a delicate golden brown. Serve at once, directly from the baking dish.