Time: 15 minutes
Cook the pasta in well-salted boiling water until al dente. Reserve ½ cup of the starchy pasta water, then drain.
Sauté the aromatics: Heat the sardine oil over medium heat; supplement with more olive oil if needed. Add the garlic and red pepper flakes, letting them sizzle for about 1 minute until fragrant.
Build the sauce: Add the sardines (breaking them up gently with a wooden spoon) and capers and heat through, about 2 minutes.
Emulsify: Add the lemon juice, lemon zest, and the butter to the pan and briskly stir in ¼ cup of pasta water. Let the mixture simmer for 2-3 minutes to create a glossy, emulsified sauce.
Toss: Add the cooked pasta to the skillet, tossing well to coat. Add more pasta water if the sauce feels dry. Remove from the heat and stir in the parsley.
Serve: Plate immediately, topping with a generous sprinkle of Parmesan.
