Purge the clams: Place clams in a large bowl of cold, salted water (2 tbsp salt per quart) for 30-60 minutes. Lift clams out, scrub shells, and discard any that are broken or won't close when tapped.

Cook the pasta: Boil spaghetti in generously salted water until 2 minutes shy of al dente. Reserve 1 1/2 cups of the starchy pasta water before draining.

Start the sauce: In a large sauté pan over medium heat, warm the olive oil. Add sliced garlic and red pepper flakes and cook for 2-3 minutes until fragrant and pale golden. Do not brown.

Steam the clams: Increase heat to high. Add clams and white wine to the pan. Cover immediately and steam for 4-6 minutes, shaking the pan occasionally, until most clams have opened.

Combine: Discard any unopened clams. Use tongs to transfer the undercooked spaghetti directly into the pan with the clams. Add 1/2 cup of reserved pasta water.

Emulsify the sauce: Add cold butter and chopped parsley. Toss everything vigorously over high heat for 1-2 minutes. The sauce should become creamy and cling to the pasta. Add more pasta water if needed to reach desired consistency.

Serve: Taste and season with salt and pepper if necessary. Divide among four warm bowls, garnish with more parsley and a drizzle of olive oil, and serve immediately.