Preheat the oven to 375F/190C.

Cut the squash in half length ways and scoop out the seeds.

Place cut side up in a roasting dish. Add the chopped garlic, a pat of butter and some thyme into the part where the seeds were then brush the neck with a little oil. Season to taste with salt and pepper.

Bake for 45 minutes to an hour or until the flesh is tender and easily pierced by a knife.

Remove from the oven and scoop out the flesh along with all of the liquids into a large bowl. Leave about a half inch on the sides so the squash holds its shape.

While the squash is roasting, melt the rest of the butter in a skillet over medium heat and cook the leeks, onion and more thyme until soft, about 15 minutes. Add the cream and continue cooking until the liquid is reduced by half. It should be very creamy.

Use a masher to break up the flesh and stir in the hazelnuts and most of the cheese. Combine with the leeks.

Transfer the filling to the empty squash halves and sprinkle with the remaining cheese. Return the squash to the oven and bake for 15 - 20 minutes or until golden and bubbly.