Preheat oven to 450º F.
Spread cauliflower florets on a parchment-lined baking sheet. Drizzle with olive oil, toss. Sprinkle with sea salt; bake for 30 minutes, stirring once.
Heat a Dutch oven over medium heat. Coat pan with cooking spray. Sauté prosciutto for 3 minutes until crisp. Remove; drain on paper towel.
Melt butter in same pan. Add onion and garlic and sauté for about 5 minutes, stirring occasionally. Add cauliflower, stock, water; bring to boil. Reduce heat and simmer for 20 minutes, stirring occasionally. Remove from heat and add cream.
Add in batches to blender and pureé until smooth. Salt and pepper to taste.
To serve, ladle into bowl, garnished with a bit of the prosciutto, a sprinkle of pumpkin seeds and chopped parsley.