Napolitan Spaghetti Recipe (Naporitan): Easy Japanese Ketchup Pasta

Add 1/2 tsp salt to boiling water and cook the spaghetti (about 9 minutes).
Drain the cooked spaghetti and mix with a drizzle of olive oil. This prevents the noodles from sticking together.
Do not discard the pasta water, as it will be used later for the pasta.
Slice the garlic thinly and slice the onion.
Cut the sausages diagonally into thin, long pieces.
Add olive oil to a pan and sauté the garlic and onion over low heat.
When the onion becomes slightly translucent, add the sausage and stir-fry.
Add 4 tbsp ketchup and 1.5 tbsp Tonkatsu sauce, stir, then add the spaghetti and 1 ladle of pasta water. Stir-fry over medium-low heat.
When the sauce is well combined, add 10 g butter and stir over low heat until melted and coated.
Plate the pasta, sprinkle Grana Padano powder, and finish with 1 pinch of parsley.