Boil the water: Bring a large pot of water to a rolling boil. Generously season with salt.
Sauté the aromatics: Heat the olive oil over medium heat. Add minced garlic and red chili flakes, sautéing for about 2 minutes.
Cook the fresh clams: Pour in the white wine and add fresh littleneck clams. Cover and steam until the clams begin to open, about 5 minutes.
Set clams aside: Remove opened clams with a slotted spoon into a bowl, leaving the broth behind.
Mix in canned clams: Drain the liquid from the canned clams and add to the saucepan, then pour in the bottled clam juice. Stir well and let simmer.
Reduce the sauce: Allow the sauce to simmer until it reduces by about two-thirds, around 5 minutes.
Cook the linguine: Add linguine to boiling water and cook according to package instructions until al dente, about 8-10 minutes.
Combine and flavor: With about 2-3 minutes left on the pasta, stir in canned clams and fresh lemon juice into the sauce.
Finish with butter: Gradually add cold, cubed butter to the sauce, stirring until creamy and fully incorporated.
Add parsley: Stir in half of the chopped parsley into the sauce.
Toss the pasta: Drain the cooked pasta and add it directly to the saucepan, tossing to coat with sauce.
Serve and enjoy: Plate the linguine in bowls, arranging reserved clams around the edges, and sprinkle with remaining parsley.