Halve 1 bunch leeks lengthwise, then cut into 3-inch pieces. Cook in a steamer basket until tender, 10 to 12 minutes. Cook 1 minced shallot in a saucepan with 1 tablespoon olive oil, 2 minutes; season with salt. Add 1 tablespoon flour and cook 1 minute. Whisk in 1 cup chicken broth and cook until thickened, 4 minutes. Whisk in 1 1/2 tablespoons dijon mustard and 3 tablespoons minced parsley. Spoon over the leeks.