Start at least a half hour ahead of time to clean the clams by putting them in a large bowl and covering them with fresh, cold water. Let them sit for about 20 minutes. Then drain and proceed.
In a large sauté pan with a cover, heat the oil over medium high heat until shimmering. Add the sausage. *See Gr8 Note
Cook, stirring, until the sausage is cooked through, about 8-10 minutes.
Add the onion and cook until translucent, about 4 minutes.
Stir in the garlic and cook about 1 minute, until the fragrance begins to release.
Pour in the wine and bring to a boil scraping any browned bits from the bottom of the pan.
Then add the clams, hot pepper flakes, and 2 Tablespoons of the parsley and stir to combine.
Cover the pan tightly and cook for 6 to 8 minutes until clams are opened. Discard any clams that don't open.
Serve directly from the pan or transfer to a serving bowl, be sure to get all the juices! Garnish with the remaining Tablespoon of parsley.
Serve with a glass of white wine and crusty Italian bread. This could also be served over pasta. Just add one cup of the hot pasta water at the end of cooking. Stir and pour over the drained pasta.