Preheat the oven to 180° prepare the cauliflower and leeks keeping the garlic whole and unpeeled. Line a baking tray with paper and place the veggies making sure they aren't too crowded. Drizzle with the oil using more if required
Roast the leeks and cauliflower for around 20-25 minutes turning half way through, remove when cooked through and turning golden though not burnt.
Remove from the oven and place in a food processor or blender popping out as many of the garlic cloves you like. I use all of them as I love garlic however, you may only want one or two. If so the others will keep in the fridge for around a week to use in other dishes. Blend until smooth with around 1 cup of the stock.
Pour this mixture into a saucepan adding remainder of stock. You may not need the 4 cups it depends if you like your soup thick or a little runny. Heat through do not boil as everything is already cooked it just needs warming. Season with salt and pepper to taste.
Serve with a splash of olive oil and herbs of your choice crusty bread or toast and enjoy.