Boil the pasta according to the instructions on the bag.
Pour the butter in a casserole and let it melt.
Add the flour in the casserole and stir it together.
Add the milk as stir until it start to boil.
Lower the heat, and squeeze a piece of garlic in the sauce.
Add the tomato puree and stir it all together.
Serve the pasta and the sauce warm, sprinkle the nuts and arugula on top of the dish.