In a large stockpot or Dutch oven of boiling salted water, cook pasta according to package instructions; reserve 1/2 cup water and drain well.
Melt butter in the Dutch oven over medium high heat. Add garlic and red pepper flakes, and cook, stirring frequently, until fragrant, about 1 minute.
Stir in vegetable broth; season with salt and pepper, to taste.
Bring to a boil; reduce heat and simmer until reduced by half, about 1-2 minutes. Stir in clams. Cover, with a tight-fitting lid, and cook until the clams have opened, about 5-8 minutes. Discard any unopened clams.
Stir in pasta and reserved pasta water, one tablespoon at a time, until desired consistency is reached.
Serve immediately, garnished with parsley, if desired.
Notes
Clean the clams first. This is key to remove sand and grit as well as exterior debris.
Cook the pasta until al dente. The pasta will finish cooking in the sauce, soaking up the briny clam juice, without overcooking and getting soggy.
Reserve the pasta water. Thanks to the starch in the pasta water, this will help the briny sauce stick to the pasta for a smooth coating.
Finish with butter. Stir in 1 tablespoon butter just before serving for a rich, shiny gloss to the pasta.
Loosen the sauce when reheating. Since the pasta will continue absorbing the sauce as it sits, add in a splash of water, white wine or clam juice to loosen the sauce.