Step 1

Fill a large bowl with cold water and stir in enough salt to make it salty like the sea. Add clams and let stand 30 minutes. Lift clams from water and discard purging water; if there is sand in the bottom of the bowl, rinse it out and repeat this process until clams no longer release sand into the water (usually 2 to 3 purging cycles). Discard any clams that are gaping open and refuse to close when prodded.

Step 2

In a large skillet, combine oil with garlic and red pepper flakes. Cook over medium heat until garlic is very lightly golden, about 5 minutes. (Adjust heat as necessary to keep it gently sizzling.)

Step 3

Add white wine and clams, cover, and increase heat to high. Cook, checking every 30 seconds or so and transferring clams as they open to a large heatproof bowl, until all clams have opened, about 5 minutes. Remove skillet from heat.

Step 4

Allow clams to cool slightly, then pull meat from shells; save a few shell-on clams per serving for garnish. If clam meat is large (for example, from larger littleneck clams), you can roughly chop it.

Step 5

In a pot or large skillet of lightly salted water, cook pasta until just shy of al dente (about 1 minute less than cooking time on package). Transfer pasta to skillet with white-wine sauce, add a few tablespoons of pasta cooking water, and cook over high heat, stirring and tossing rapidly, until sauce has reduced and is beginning to form a creamy, emulsified coating on the noodles. Add butter, if using, and both clam meat and shell-on clams. Cook, stirring, until butter is melted and clams are heated through, about 1 minute; add more pasta water, 1 tablespoon at a time, if sauce over-reduces and becomes dry or greasy. Season with salt if necessary. Remove from heat.

Step 6

Stir in parsley and a drizzle of fresh olive oil. Transfer to bowls and serve right away.