Peel the loose paper away from the heads of the garlic and discard. Trim about ¼” - ½” off the top of the garlic to expose the garlic cloves. Drizzle the garlic with 1 tablespoon of the olive oil. Wrap the heads of garlic in aluminum foil.
Toss the cauliflower florets in 2 tablespoons of olive oil then season with salt and pepper. Spread evenly on a baking sheet. Add the garlic to the pan.
Roast until the cauliflower is tender, about 30 minutes. Set aside. Return the garlic heads to the oven and continue to roast until the cloves are soft when pierced with a knife, about an additional 15 minutes.
Heat a large heavy-bottomed pot or Dutch oven over medium heat, add the remaining olive oil and heat through. Add the onion and sauté until tender, about 6 minutes.
Add the roasted cauliflower, thyme and wine, simmering until the wine has reduced by half. Add the chicken stock and bring to a boil, then lower heat to medium-low, simmering for about 20 minutes. Season to taste with salt.
Let cool slightly then squeeze the roasted garlic cloves from the skin into the soup. Puree the soup in batches using a blender or an immersion blender.
Return the soup to the pot and keep over medium-low heat. Stir in the heavy cream and lemon juice. Season with salt and pepper to taste. Slowly stir in the Parmesan until the cheese is completely combined.
For the crispy pancetta and toasted breadcrumb topping:
Heat a medium skillet over medium heat, add the pancetta and cook, stirring occasionally, until crispy, about 6 minutes. Remove from the pan and set aside in a bowl.
Leave about 1 tablespoon of the fat in the pan and turn down the heat to medium-low heat. Add the butter to the pan and allow to melt.
Add the breadcrumbs to the pan stirring to combine. Let cook, stirring constantly, until the breadcrumbs are golden brown. Remove to a small mixing bowl and stir together with the pancetta, parsley and pumpkin seeds.
To serve:
Ladle the soup into warmed soup bowls and top with the crispy pancetta and toasted breadcrumb topping.