Start heating the oven to heat to 200 C / 400 F / Gas Mark 6.
Quarter and seed the squash. Leave the rind on.
Space the squash quarters out in a casserole dish (no need to grease), and cook for 30 minutes.
Meanwhile, in a small saucepan melt the butter with garlic. Cook for a minute, stir in the sage, garlic, salt, pepper, and 2 tablespoons of white wine, and cook for another minute. (Don't let it brown.) Set aside.
In a small dish, thin the sour cream with the final tablespoon of white wine, and a few grates of nutmeg. Set aside.
After 30 minutes, remove the squash briefly from the oven, and brush the above sauce over the tops and sides of the squash pieces and then return the squash to the oven to cook for another 15 minutes, or until the squash is tender to a fork.
When the squash is tender, remove the squash briefly from the oven, and brush the cream sauce over the tops and sides of the squash. Sprinkle a tablespoon of grated cheese on each squash quarter, along with half a tablespoon of parmesan. Put under the broiler for 2 to 3 minutes or until the cheese is bubbly and golden.
Serve piping hot.