Rinse and scrub clams to remove sand and grit. If you have time, purge the clams in 1 quart of cold water with 2 tbsp + 1 tsp of sea salt for at least an hour. Bring a large pot of salted water to a boil. Place a large saucepan over medium-low heat, add 5 tbps olive oil, 3 cloves garlic, minced and a pinch of red chili pepper. Sauté gently until garlic is a golden in color. Add 1/2 c dry vermouth and clams, and cover. Raise heat and carefully shake pan occasionally. Clams should open in 2 to 4 minutes. Remove clams and place into a bowl as they open to avoid overcooking. While the clams are cooking, add the spaghetti to boiling water and cook until slightly undercooked. Drain pasta and add to the sauté pan once all clams have opened, returning any clams and their juices to the pot and removing any clams that have not opened. Add remaining olive oil and 1 tbsp butter and over low heat, toss for 1 to 2 minutes. Adjust seasoning if necessary and add additional oil if needed. Add parsley and give a final toss before serving.