To make vegan or dairy-free, replace butter with your favorite plant-based butter and cook the same way., Store leftovers in an airtight container in the fridge for up to 5 days., Ensure leeks are cleaned thoroughly to remove any dirt trapped between layers; slice first and soak in cold water, then drain., Add lemon juice near the end of cooking to brighten flavor and prevent butter from curdling., For extra silkiness, stir in a small bit of butter or olive oil off the heat before serving., Optional variations include adding mushrooms, bacon, pancetta, white wine deglaze, creamy finishes, fresh herbs, spices, crispy toppings, or parmesan cheese., Reheat gently on stovetop, microwave, or in oven to maintain moisture.