Put chiles in a bowl and cover with boiling water. When they are rehydrated, drain them and put them in a food processor or blender; process until finely chopped.
In a small saucepan over medium-high heat, melt butter.
With machine running, add hot butter to chiles in a fine stream. Blend until color is homogeneous and mixture is smooth.
Let stand at room temperature until butter reaches a spoonable consistency. Use immediately, or refrigerate or freeze for later use.
Complete step 1.
Put butter in a glass dish and microwave on 100% power until butter is melted, about 45 to 60 seconds.
Continue with steps 2 and 3.
Makes 1/2 cup.