Preheat the oven to 375 degrees.
Chop the potatoes (I left the peel on) and Romanesco cauliflower into roughly 1 inch pieces.
Toss them lightly in olive oil and spread them on a baking sheet. Roast for 15 minutes or until the cauliflower is slightly browned on the edges and a fork can be easily inserted into the potatoes
After the potatoes and cauliflower are cooked, add them to a soup pot along with the vegetable broth and salt and pepper to taste.
Bring the mixture to a boil.
Remove the soup from the heat and use an immersion blender to puree about half of the soup (more or less, to taste). Stir in the heavy cream.