Heat the butter in a large sauce pot over high heat. Whisk often so the butter doesn't burn on the outside of the pan. The butter will start to bubble and froth up. Whisk often at this point. The butter will start to darken and turn brown. Remove from heat and keep whisking.
Add the cream cheese.
After a minute, slowly add the broth, truffles and salt.
Use a stick blender to puree until smooth. Taste and adjust seasoning and truffle taste to your liking.
Pour into a mason jar. Cover and store in the fridge for up to 7 days. This sauce will thicken a lot overnight.