Preheat the oven to 400 F.
To prepare the leeks, cut off the root and the tip. Slice each leek lengthwise, and wash under running water between the leaves to remove any extra grit.
Bring ½ cup of water to a simmer in a large pan or skillet. Place the leeks cut-side down in the water, and allow to simmer on medium-low heat until the leaves become slightly softened, about 5 minutes.
Remove the leeks from the water, and arrange them in an ungreased baking dish in a single layer.
Sprinkle the leeks with salt and pepper. Drizzle the melted butter and Parmesan cheese evenly over the tops.
Place the baking dish in the oven, and allow to bake until the leeks are fork tender and the Parmesan crust has turned golden, about 25-30 minutes.
Remove from the oven and serve the leeks on a large serving platter. Garnish with fresh, chopped parsley or more Parmesan cheese (optional). Serve 1-2 halves per person.
Pro-tip: It is essential to clean your leeks before you prepare them, as more often than not, there's extra dirt and grit between the leaves. Be careful!