For the chili butter, remove the butter from the refrigerator in time to make it smooth. It is best to put the butter on a parchment or buttered paper and spread it a bit.
Add the spices and, using the back of a knife, brush the butter back and forth to combine.
Be sure to leave covered at room temperature for 2 hours so the flavor can really develop. In the refrigerator, the butter becomes hard again relatively quickly and the butter can not develop.