Bring water to a boil. I usually use 15 grams of salt per liter of water. Here, I boiled it in 2 liters of water, so I used 30 grams of salt.
Grate the Parmesan into a bowl.
Cut the butter into smaller pieces.
Put the pasta in the water and cook it 1 minute less than the package instructions.
Put butter and half of the Parmesan in a sauté pan and melt it over low heat, stirring regularly.
When the pasta is done, remove it from the boiling water with a pasta spoon and transfer it directly to the sauté pan, ensuring some of the cooking water comes along.
Turn off the heat and stir well continuously for 1-3 minutes while adding the rest of the Parmesan.
The cheese sauce will now cling to the pasta thanks to the starch in the cooking water (the flour from the pasta comes out in the water). Add a bit more cooking water if it doesn't cling well to the pasta.
If you are not comfortable with this method, you can drain the pasta in a colander. Just make sure to place a coffee mug/bowl underneath to save some of the cooking water for the sauce.
If you don't have a sauté pan, you can simply strain most of the water from the pot with the pasta and add the butter/Parmesan.
Serve immediately with a bit of freshly grated Parmesan and optionally lots of freshly ground pepper on top.
Enjoy your meal.