Bring a large pot of salted water to a boil. Cook the pasta according to package directions. Once al dente, reserve ½ cup of the pasta water, then drain.
Dry shrimp with a paper towel. Season with salt and pepper on both sides.
Add oil to a large skillet on medium-high heat. Once the pan is hot, sear the shrimp 30 seconds on each side. Remove from the pan, and set aside
To the pan, add 2 tablespoons of the butter. Once melted, sauté garlic and shallot for 1-2 minutes, or until caramelized.
Add the fresh basil and crushed red pepper. Stir and cook for 2 minutes.
Gently pour in the vegetable stock, lemon juice, and zest. Stir occasionally, cook until the volume of the liquid is reduced by half.
Turn the heat to medium, and stir in the remaining butter.
Fold the shrimp, crab, parsley, pasta, and reserved pasta water into the butter mixture. Cook for 2 minutes. Add salt and black pepper to taste.
Serve and garish as desired.