Preheat the oven to 400 degrees.
Spread the potatoes, onions on a roasting pan lined with foil. Nestle the garlic on top.
Sprinkle the vegetables with rosemary, salt and pepper and drizzle with olive oil.
For 45 minutes or until potatoes are fork tender and garlic is brown but not burned.
Once the garlic has cooled slightly, remove the cloves from the skins.
Add the garlic and half the vegetable mixture to a blender.
Whisk together the broth and flour. Pour into the blender and blend the mixture slightly, leaving a few lumps.
Pour the blended mixture into a stockpot. Add the remaining vegetables, and broth.
Stirring frequently, cook over medium-low heat, adding the heavy cream ¼ cup at a time, until thickened.
Serve in bowls, garnished with fresh rosemary.