Preheat an oven to 200°f / 100°c. Place a large ceramic mixing bowl inside the oven.
Bring water (about 1 liter or 1 quart) with the salt to boil in a medium-sized saucepan. Once the salted water is boiling, drop in the pasta and cook according to instructions, stirring constantly.
During the last minute of pasta cooking, pull the ceramic bowl from the oven. Place the softened butter into the heated bowl and flatten the butter with your hand or a spoon.
Reserve about a cup of water from the pasta pot using a heat-proof measuring cup. Remove the cooked pasta from the pot with either tongs or strain it through a colander and immediately place the pasta into the bowl with the butter. (If using a colander, immediately transfer the pasta to the bowl after straining it.)
Mix the pasta with the butter, adding about 1/4 of the pasta water. Keep mixing until the butter begins to thicken at the bottom of the bowl. Add the Parmigiano-Reggiano about a quarter at a time and mix, adding the remaining pasta water to the bowl, until the sauce reaches a desired thickness and consistency.
Serve in small pasta bowls. Optionally garnish with fresh parsley.
Notes
Grate the Parmigiano-Reggiano cheese using the small diamond setting of your grater for best results.
We recommend dry egg pasta for the best consistency and results.