Step 1
Preheat oven to 425°. Crush 8 garlic cloves with the flat side of a chef's knife and remove peel. Cut ¼ cup (½ stick) butter into small pieces (about ½").
Step 2
Empty 28 oz. can of tomatoes into a 13x9" baking dish and crush lightly with your hands. Watch out for flying tomato juices. Scatter garlic, butter pieces, 2 anchovies, and ½ tsp. red pepper flakes over tomatoes; season with salt and black pepper.
Step 3
Roast tomatoes, tossing halfway through, until garlic is very soft and mixture is thick and jammy, 35–40 minutes. While tomatoes are roasting, bring a large pot of water (4-6 qt.) to a boil over high heat and add a small fistful of salt.
Step 4
Remove pan from oven and let sauce cool slightly. Using a potato masher or fork, break up garlic and tomatoes until mixture looks like coarse applesauce.
Step 5
Cook 12 oz. bucatini or spaghetti in pot of boiling water, stirring occasionally with tongs, according to package instructions for al dente. Toward end of cook time, use a heatproof measuring cup to scoop out and reserve ½ cup pasta cooking liquid. Drain pasta in a colander; reserve pot.
Step 6
Return pasta to pot and add tomato sauce and pasta cooking liquid. Cook over medium-high heat, tossing with tongs, until sauce coats pasta, about 3 minutes.
Step 7
Divide pasta among plates. Serve topped with Parmesan and more red pepper flakes.
Step 8
Do Ahead: Tomato sauce can be made 4 days ahead. Let cool; cover and chill. Reheat before mixing with pasta.
