Combine pistachio cream, sugar, heavy cream, and milk in a saucepan. Bring mixture to a boil while constantly stirring. Take the pan off stove and let mixture cool completely.
Once cooled, stir in alcohol. Pour liqueur into an airtight container, jar, or bottle. Secure lid and refrigerate for at least one day before serving. It will keep for up to 3 weeks in refrigerator.