Line a large baking sheet with parchment paper. Place a rack in the middle of the oven and preheat it to 220 °C / 430 °F.
Peel the butternut squash, cut in half, remove the seeds and cut it into 2cm or 1-inch chunks. Add the squash to the prepared baking sheet. Season with olive oil, salt, pepper, and thyme. Stir, then arrange in a single layer. Add halved head of garlic and place in the oven. Roast for 15 minutes at 220 °C / 430 °F.
COOK THE ONION AND CELERY
Peel the onion and celery, then finely dice it. Set a large skillet or pot over medium-low heat. Add the olive oil, diced onion, diced celery, and saute for 8 - 10 minutes, stirring occasionally.
SQUASH AND PROSCIUTTO
After 15 minutes, carefully take the baking pan with squash from the oven. Place the prosciutto on top and place it back in the oven. Roast for another 8 - 10 minutes or until the squash is soft and prosciutto golden-brown and crunchy.
add the rice
Increase the heat and add the rice to the veggies. Stir and cook for 2 - 3 minutes. Pour in the wine, and cook for another 2 - 3 minutes for the alcohol to evaporate. Gradually, ladle by ladle, start adding the vegetable stock. Add the next ladle of stock only when the first one is cooked into the rice. Repeat the process until the rice almost cooks. It will take about 15 - 18 minutes. Make sure to stir the risotto regularly.
butternut squash risotto
Transfer the roasted butternut squash to a blender or bowl. Peel the garlic, and add to the squash along with the butter. Mix into a creamy mixture using a blender or an immersion blender. Pour in the milk and blend until creamy and combined. Stir the squash puree into your risotto. Remove from the heat and stir in the shredded parmesan cheese. Season to taste with salt and pepper. Divide the risotto between four plates and serve with crispy prosciutto.