In a large pot, heat butter over med-high heat and add sliced leeks, garlic, bay leaf and paprika and cook for a couple of minutes until leeks are tender but not browned. Add a couple of tablespoons of stock if leeks are sticking to the pot
Add diced potatoes, parsley, black pepper and stock. Cover and bring to the boil. Cook for around 15 minutes or until potatoes are soft.
Add spinach and cook for a couple more minutes until wilted.
Remove from heat and blend with a stick blender until all lumps are gone and the soup has a smooth consistency.
Place pot back on the heat and add milk, white pepper and nutritional yeast, simmer uncovered for 5 minutes until soup is thick and warm.
Serve warm with chopped parsley and warm bread or refrigerate and serve cold.