Warm a saucepan over medium heat and add the tablespoon of water.
When it begins to boil, add butter, one tablespoon at a time, whisking constantly. Wait until the previous addition of butter is fully melted and incorporated to add the next.
Reduce the heat if necessary to ensure that the butter does not boil. Keep warm over very low heat until ready to serve.
Boil pasta according to package instructions in heavily salted water. When the pasta is finished, toss it with the burro fuso and serve immediately.