Melt butter in a large pot over medium heat. Cook and stir onion, leeks, garlic, salt, and pepper ,celery and carrots in the hot butter until veggies are tender , about 15 minutes.
add water and soup base.pour over leeks . Add potatoes to the broth mixture and bring to a boil; season with onion powder and garlic powder. Reduce heat, , and simmer until potatoes are tender, about 30 minutes.
Remove pot from heat and blend soup using a hand blender until smooth; season with salt and pepper. set in fridge , next day bring to simmer and add roux(flour and butter)to thicken soup,add cream, if to thick just add some milk to thin out