Cook the pasta in a pot of boiling salted water until just tender. Reserve 1/2 cups of the pasta water then drain the pasta.
While the pasta is cooking, heat the butter in a large non stick pan, when hot, add the anchovies and garlic. Cook and stir often, mashing up the anchovies, they dissolve into the butter, until the garlic is tender, about 4-5 minutes.
Add the tomatoes and season with salt and pepper as desired, stir occasionally and cook down the tomatoes until they are falling apart, about 10 minutes or so.
Add the pasta to the pan plus the reserved pasta water and toss with the tomatoes. Cook until the all the pasta is coated with the butter sauce and the pasta is heated through.