Melt the margarine in a large saucepan over medium-high heat. Add the sliced leek, and sauté 4 minutes. Add the hash brown potatoes and next 5 ingredients (potatoes through spinach). Bring to a boil; reduce heat, and simmer 5 minutes, stirring occasionally.
Place half of potato mixture in a food processor or blender, and process until smooth. Pour puréed potato mixture into a large bowl. Repeat procedure with remaining potato mixture. Return puréed potato mixture to pan. Stir in cheese and milk; cook 1 minute or until thoroughly heated and cheese melts.