Set a large sauté pan over medium heat. Add the butter, diced onion, and garlic. Sauté for 2 to 3 minutes to soften the onions. Make sure not to burn the garlic and onions, if needed turn the temperature down just a little.
Stir in the shrimp and cooking sherry. Continue to sauté for 2 to 3 more minutes until the shrimp are mostly cooked through.
Add the tomato sauce. Bring to a simmer and cook another 7-10 minutes.
Turn off the heat and stir in the basil leaves. Taste, then salt and pepper as needed. Allow the seafood marinara to rest for 20+ minutes before serving, so the seafood flavors can intensify without overcooking the shrimp. (I usually make the sauce first, then boil the water for the pasta, or shred the noodles. Then I rewarm the sauce if needed.)
Notes
Allow the seafood marinara to rest for 20+ minutes before serving, so the seafood flavors can intensify without overcooking the shrimp.Serve the red sauce with shrimp over traditional pasta, or with healthy zucchini noodles.This recipe is made with shrimp, but can be adjusted to include other types of seafood. Try it with scallops or clams!If the tomato sauce seems a bit acidic, stir in 1 teaspoon of sugar.