Microwave or cook spinach and remove all excess water. Cool spinach.
I like doing this in a stand mixer. If you don't have one, just make this in a large bowl. Put the spinach in a bowl. Add finely chopped onions and butter and nutmeg. Add beaten eggs. Gradually add dressing and mix thoroughly. If you feel the mixture is too moist and will not form a ball, then add more stuffing mix. Mix in cheese gradually.
Using a small ice cream scoop, shape into 1 inch balls and place on a sheet pan lined with parchment paper or Silpat.
Bake for 15 minutes or until the balls have started to brown.
Notes
You can add sun-dried tomatoes or pine nuts if you want.
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