In a Dutch oven, warm the olive oil over medium-high heat.
Add the garlic and cook until golden, about 1-2 minutes.
Add the chili flakes and cook for 30 seconds more.
Add the tomato puree and salt, cover with lid, and cook until the oil separates and the sauce has thickened, 10-12 minutes.
Remove lid, add water, and remove from the heat.
In a large pot of well-salted boiling water, cook the pasta according to the package instructions until 2 minutes shy of al dente; drain.
Toss the bucatini into the Dutch oven with the tomato sauce, herbs, and butter. Cook over medium heat until the pasta is just al dente, 1 to 2 minutes.
Stir in the parmesan and pepper, adding more water if the sauce seems dry.
Divide the pasta among individual serving plates or bowls and finish each with 2 teaspoons or more of parmesan Romano and a drizzle of olive oil.