Set the oven to 200 degrees Celsius (390 degrees Fahrenheit)
Cut the cauliflower into medium sized pieces and cut the leeks in 2 inch slices. Cut the top 1/3 off of the head of garlic to expose the top of the cloves. Place the garlic along with the leeks and cauliflower on a baking sheet. Season with salt and drizzle the olive oil over top.
Place in the oven and cook for 20 minutes until the cauliflower is tender and has begun to brown. Half way through cooking remove the pan from the oven and flip the vegetables to ensure they don't get too dark on one side.
Once cooked remove from the oven and put the cauliflower, leeks and garlic in a blender. Add in the lemon juice, smoked paprika and 2 cups of the chicken/vegetable stock and blend.
Once smooth, pour the soup into a pot on the stove on medium-low heat and add the remainder of the stock slowly until the soup reaches your desired consistency. Season with salt and pepper.
To serve ladle the soup into a bowl and top with a sprinkling of pancetta/pumpkin seeds. If you want to be fancy, you can drizzle truffle oil over top before serving. Enjoy!