In a food processor or mini prep fitted with a steel blade combine the maple syrup, vinegar, shallots, mustard, salt and pepper and process until combined.
If not using a food processor or mini prep for the dressing, whisk together the syrup, vinegar, shallots, mustard, salt and pepper and then add the oil in a steady stream while constantly whisking.
Stir in the poppy seeds when the dressing is emulsified.
Spinach Salad:
Combine all the salad ingredients in a large bowl and toss with as much dressing as desired.