Melt margarine in a pot.

Saute chopped onions and celery in the margarine until translucent.

Add diced potatoes, water, parsley, salt, pepper, chicken bouillon cubes, and thyme to the pot.

Cook until potatoes are tender, about 20-25 minutes.

Remove half of the mixture from the pot.

Blend the removed mixture until smooth using an immersion blender or regular blender.

Return the blended mixture to the pot.

Bring the soup to a boil.

Add evaporated milk.

Simmer for 10 minutes, stirring occasionally.