Cook linguine in a large pot of salted boiling water until it's about a minute shy of al dente, about 8 minutes (pasta will finish cooking in the clam sauce and should have a little firmness to it).
While the pasta is cooking, heat 1/4 cup of olive oil in a deep skillet, sauté pan, or braiser (12-14 inches wide). Add garlic and red pepper flakes and cook, stirring, until garlic is lightly-browned and fragrant, about 1-2 minutes.
Add white wine, lemon juice, and clams, cover pan, and steam over medium-high heat until clamshells have opened, about 5-8 minutes. Gently shake the pan occasionally. I like to start checking the clams at the early end of the range, transferring them from the pan one at a time to a holding bowl as they cook. For tender clams, it's important not to overcook. Tent the bowl of cooked clams with foil. (A few clams might need a little extra time. Discard any clams that don't open after 10-13 minutes.)
Reserve 1/2 to 1 cup of pasta water before draining the linguine. When all of the clams are cooked and removed from the pan, whisk 3 tablespoons of butter into the simmering steaming liquid.
Add the drained linguine to the pan, tossing to coat. Cook for about 2 minutes, until linguine is al dente. The sauce should be brothy, but will lightly cling to the noodles. If the linguine looks dry at any point, stir in some of the reserved pasta water, as needed.
Stir the chopped parsley into the pasta. Season to taste with salt*, additional red pepper flakes, and lemon juice**, if needed.
At this point, you can either remove the clams from their shells and stir the meat into the pasta, or serve the pasta tossed or topped with the whole clams for guests to de-shell in their bowls. We like to remove the meat from about half of the clams and leave half whole.
Garnish the dish with a drizzle of fruity olive oil, fresh lemon wedges, and the remaining parsely. Serve immediately with crusty bread for dipping.
Manila clams can be substituted for littlenecks, but they will take less time to steam open, 3-4 minutes total.*The amount of kosher you'll need depends entirely on your clams. There have been times I've added upwards of a full teaspoonful of salt to the pasta before serving, and times when I've only needed a pinch.**We love the bright flavor that 1/4 cup of lemon juice adds to the sauce. If you prefer less lemon, start with 2 tablespoons when steaming the clams, adding additional to the pasta in step 7, to taste.