Step 1

Bring 3 quarts water to boil in large Dutch oven. Add pasta and 1 tablespoon salt and cook, stirring often, until strands are flexible but still very firm in center, about 5 minutes. Turn off heat, reserve 3 cups cooking water, then drain pasta.

Step 2

In now-empty pot, heat oil and garlic over medium-low heat until fragrant and just shy of browning, 2 to 3 minutes. Stir in capers and pepper flakes and cook until fragrant, about 20 seconds.

Step 3

Add pasta, 2 cups reserved cooking water, and salt and bring to boil over medium heat. Cook, stirring often with tongs and folding pasta over itself, until water is mostly absorbed but still pools slightly at bottom of pot, about 5 minutes.

Step 4

Off heat, stir in tuna, Parmesan, parsley, and ½ cup reserved cooking water with tongs until all ingredients are well combined, about 1 minute. Adjust consistency with additional reserved cooking water as needed. Serve, sprinkled with extra Parmesan and pepper flakes and drizzled with extra oil.