Preheat oven to 180C/350F.
In a baking dish/tray, throw in your broccoli, onion, garlic, chilli flakes, salt, pepper and a generous drizzle of olive oil. Bake for around 1 hour or until the veggies are soft and slightly browned. Reserve a few broccoli pieces for garnish.
In a pot, melt 2 tbsp of butter and throw in the leeks. Sweat the leeks until they are soft and translucent.
Add into the pot the potato, roasted veggies, squeeze in the roasted garlic and stock. Cover and bring to a boil. Continue cooking until the potato cubes are fork-tender.
Meanwhile, prepare the croutons, Line the bread slices into a single layer on a lined baking tray and grate over with cheddar. Put it until the broil for roughly 5-10 minutes or until the croutons are golden.
Once all the veggies are cooked, blend up the soup until smooth. Season with salt and pepper to taste. Serve with cheddar croutons.