Trim stems off of the spinach, chop it and rinse well. In a large skillet, add spinach and onions over low-medium heat. Steam covered for about 10 minutes stirring occasionally. Remove spinach mixture from the skillet and set aside. While spinach is cooling, heat olive oil or butter over medium heat. Once heated through add flour, (1 T. at a time) mixing thoroughly with the oil or butter making sure there are no lumps. Reduce heat to low and once more finely chop the spinach-onion mixture with the garlic clove and add it to the oil-flour mixture. Mix very well then add the buttermilk, salt and nutmeg. Mix well and allow to remain on the heat for another 5-10 minutes.