Reserve about 1/4 cup of the sliced leeks and put the rest in crockpot. Add potatoes, stock, dill, salt, and pepper. Cover and cook on low heat for 6-8 hours, or until potatoes are tender.
Puree soup using an immersion blender or use a potato masher. Note: Immersion blender will make a creamier soup. Add yogurt to soup and stir until smooth.
Before serving, heat olive oil in a skillet over medium heat. Add leeks and paprika. Sauté leeks until golden and crisp. Ladle soup into bowls. Serve topped with sautéed leeks.