Spaghetti with Mussels, Squid Ink, and Breadcrumbs

Heat a large heavy-bottomed pot or Dutch oven over medium-high until hot. Add mussels and 1/2 cup water (mussels should sizzle when they hit the pan). Cover and cook, shaking pot occasionally, until mussels have opened, about 4 minutes. Remove from heat; discard any mussels that have not opened. Remove mussel meat from shells, and place on a plate lined with paper towels; discard shells. Gently pat meat dry, and set aside. Bring wine to a boil in a small saucepan over medium-high. Boil until wine is reduced to about 1/4 cup, about 3 minutes. Remove from heat. Place mussel meat, Dijon, salt, and reduced wine in a 2-cup liquid measuring cup or bowl with tall sides. Process with an immersion blender until smooth, about 30 seconds. Add egg yolks and, if using, cuttlefish ink, and process until creamy, about 30 seconds. Set mussel mixture aside. Melt lard in a medium skillet over medium. Add breadcrumbs, and stir until breadcrumbs are moistened. Cook, stirring often, until crunchy and brown, about 4 minutes. Remove from heat; season with salt to taste, and set aside. Cook pasta in a large pot of salted water according to package directions for al dente. Meanwhile, heat oil in a large, deep skillet over medium. Add garlic, and cook, stirring constantly, until garlic is golden, about 3 minutes. Remove from heat. Using tongs, lift cooked pasta from pot, and transfer to skillet with garlic, reserving cooking liquid in pot. Add mussel mixture to pasta mixture, and toss to coat. Add reserved cooking liquid, 1 tablespoon at a time, as needed to loosen sauce. Season with salt to taste. Divide pasta mixture among shallow bowls, and top evenly with toasted breadcrumbs.