Whisk together vinegar, maple syrup, chopped shallots, dijon mustard, and sumac in a small bowl.
Slowly pour in olive oil, whisking constantly.
Add salt and pepper, and whisk together.
Notes
Storage: Sumac Dressing can be refrigerated in an airtight container for up to a week. Expert Tips: Adding the olive oil after you have whisked the rest of the ingredients together helps you build an emulsion in the dressing. Adding the olive oil slowly, while whisking, will also help. Add more maple syrup if you like it sweeter, or more ground sumac for a more intense flavor.