Place onions, garlic, leeks, potatoes and carrots into a large pot with butter over medium heat. Sweat off until softened, about 10 to 15 minutes.
Add the liquids (stock and milk) and simmer for approx 45 minutes.
Add herbs and seasoning to taste and cook through for a further 10 minutes.
Liquidise or use a hand held blender and then heat through once more.
Serve with fresh bread and enjoy!