Blanch spinach in boiling water for 1 minute. Then place spinach into ice water bath to cool.
Once spinach is cooled, drain. Place the bunch of spinach in your hands and form into a ball, squeezing out any excess liquid. Then set aside.
Heat a medium size skillet on medium heat. When pan is hot, add in oil and sliced onions, mixing thoroughly into the oil. Place a lid on the onions, turn fire to medium low and allow onions to slowly caramelize for 5 minutes. Check on onions and mix with a spatula. For more caramelization, place lid on and allow onions to cook another 5 minutes.
Then add in garlic to the onion mixture. Cook for 2-3 minutes. Then add in cream, nutmeg, pepper, and Parmigiano Reggiano.
Add drained spinach and mix well into the sauce. Add salt to taste.
