Preheat the oven to 400°F (200°C). Cut the pumpkin or butternut squash in half, scoop out the seeds, and score the flesh with a knife. Place the pumpkin halves on a baking sheet.

Cut the garlic head in half horizontally, rub the cut garlic over the surface of the pumpkin, and place the garlic halves and sprigs of rosemary or thyme in the pumpkin cavity. Drizzle with olive oil and sprinkle with salt. Roast for 45 minutes or until the flesh is tender.

While the pumpkin is roasting, prepare the walnut crispies. In a small bowl, mix the melted butter, brown sugar, cayenne pepper (if using), kosher salt, and black pepper. Set aside.

After 45 minutes of roasting, add the chopped walnuts to the baking sheet and roast for an additional 8–10 minutes, until the walnuts are toasted.

Remove the baking sheet from the oven. Toss the toasted walnuts with the butter and brown sugar mixture directly on the baking sheet. Set aside.

Remove the herbs from the roasted pumpkin. Scoop out the flesh into a blender, adding 3–4 roasted garlic cloves. Add about 1 cup of broth and blend until very smooth, adding more broth if needed to reach your desired consistency.

Transfer the pureed soup to a pot over medium heat. Stir in the half-and-half or cream (if using) and season with salt to taste. Heat until warmed through.

Serve the soup hot, topped with walnut crispies, shredded Gruyère cheese, and kale chips (if using).