Spinach & Parmesan Gratin

I was torn whether to put this into my healthy recipes or not, but it all depends on how you make it. I will write down the options. Everyone in my family loves this dish. I have made it with fried chicken & with steak. There are richer versions out there with lots more cheese but I like the simplicity of this one. I may reduce the parmesan cheese to 1 cup next time, putting in 3/4 with the mixture & sprinkling the 1/4 on top. It's so wonderful!

2 lbs fresh spinach - (3) 10 oz bags. I leave the stems on.
1 1/2 cups of milk (I used 1% or 2% last time I wanted to make a low-fat version & it was great)
2 tblspn olive oil (original recipe called for 2 tblspn unsalted butter, and more for baking dish)
1/2 medium yellow onion, diced
2 tblspn all purpose flour
1/2 tsp kosher salt, pinch of freshly ground pepper, pinch of ground cayenne
1 1/2 cups of parmesan cheese, freshly grated or jarred

Heat oven to 350. Lightly oil a baking dish and set aside. In a large saucepan heat an inch or two of water. Add the spinach in large handfuls, adding more as it wilts. I do it in batches. Blanch each batch for one minute. Run under cool water. Drain and squeeze as much water out. Chop coarsely (I do it right in the colander).

Heat the milk in the microwave until hot. Set a medium saucepan over medium heat with the olive oil. Add the onion and cook for 5 minutes. Stir in flour, salt, pepper and cayenne and cook, stirring constantly for 2 minutes. Slowly stir in the milk and cook until the sauce bubbles and thickens, stirring frequently, about 5 minutes. When sauce is ready, stir in 1 cup of parmesan cheese and combine well. Take off heat. Stir in chopped spinach and mix well. Taste and season with more salt if needed. Maybe add some garlic powder which I did once. Scrape into baking dish and sprinkle the remaining parmesan cheese on top. Bake 35-40 minutes until gratin is nice and bubbly and brown on top. Let cool a few minutes before serving.