Preheat oven to 200°C (400°F). In a large saucepan of boiling salted water, cook turnips for 20 minutes or until soft. Cool in ice water. Cut turnips in half and scoop out 4 turnips, leaving 4 sturdy shells. Mash all turnip.
In a frying pan, melt butter over medium heat and cook turnip and shallot for about 5 minutes. Add raisins, cream, thyme and half of cheese. Salt and pepper, to taste.
Arrange turnip shells in a buttered ovenproof dish; stuff each shell with turnip mixture, dividing evenly.
Sprinkle remaining cheese on top. Sprinkle with nutmeg, to taste, and bake for 10 minutes until cheese is melted and golden.