1. Bring carrots and milk to a boil in a medium saucepan over medium heat. Reduce heat to low, and stir in sugar and next 3 ingredients. Simmer, stirring often, 25 minutes or until carrots are tender.
2. Transfer mixture to a blender, reserving 1/2 cup cooking liquid. Add butter and orange zest to carrot mixture, and process until smooth, stopping to scrape down sides as needed. Add reserved cooking liquid, if necessary, 1 Tbsp. at a time, and process to desired consistency. Serve immediately or chilled. Refrigerate in an airtight container up to 3 days.
Note: Organic milk may curdle while simmering. Don't worry, it will smooth out when processed in the blender.