Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-12 minutes or until tender. Drain. Mash 2 cups potatoes; set aside.
In a Dutch oven, saute leeks in oil until tender. Whisk the flour, bouillon granules and broth until smooth. Gradually stir into pan. Add milk. Bring to a boil; cook and stir for 2 minutes or until thickened.
Stir in mashed potatoes. Add spinach, salt, pepper and remaining potatoes; cook just until spinach is wilted. Sprinkle with cheese.