Gourmet Cheese Sauce

I had the hardest time trying to come up with a name for this sauce.... Onion and Garlic Cheese Sauce, Cheese Sauce with Onion, Cheese and Onion Sauce with Garlic.... whatever. I thought that the word "Gourmet" just covered all of it, so there you go.  This sauce just really hit the spot with our dinner tonight.  We served this over some steamed white rice, but you can just as easily have it over pasta, or serve as a dipping sauce.
(I know I say to try and use oil instead of butter when cooking, but I think that is is one of those times that butter is better for the consistency of the dish)

1 whole onion, diced
6 garlic cloves, crushed and minced
2 handfuls of spinach, chopped
2 Tbsp. oil
2 Tbsp. butter
2 Tbsp. flour
1 1/2 cups of milk
1/2 tsp salt
1/2 tsp pepper
1 cup mozzarella or swiss, shredded
1/4 cup of romano cheese, shredded
1/4 cup parmesan cheese, shredded

Begin by melting butter in a saucepan over medium heat

  

Meanwhile, pour oil into frying pan over medium heat. Add garlic, onion, and spinach. Saute until onion is soft and translucent. Remove from heat. (you may be multi-tasking between both burners here)

Once butter is melted, add flour, salt and pepper. Stir in flour and seasonings until mixed well, making a roux.

Slowly add milk and stir briskly to combine roux mixture.  Turn heat to medium-high.

Bring milk mixture to a boil. Let boil for 30 seconds.

Add all cheeses and stir until melted.

Once cheese is melted, add sauted mixture to the saucepan

Stir until everything is well combined

And serve!