Wash the butternut squash, cut in half, remove the seeds, and dice.
Peel and finely chop the shallot. Melt half of the butter in a saucepan, sauté the shallot for 2 minutes over medium heat, then add the butternut squash. Sauté for 3 minutes, season with salt and pepper, then cover with enough water and continue to simmer for 20 minutes. Blend the mixture with the double cream.
Clean the cep mushrooms, cut them in half or quarters depending on their size. Melt the remaining butter in a skillet, sauté the cep mushrooms for 5 minutes, season with salt and pepper.
Prepare the soup in bowls or deep dishes, add the cep mushrooms, and top with truffle shavings.