Pour olive oil in a Dutch oven and heat. Add the garlic and lightly brown. Add in the spinach, one bag at a time until it has wilted but still has some fresh quality. Set aside.
In a separate saucepan, melt the butter. Add the flour in a slowly and stir until dissolved. Add the milk slowly and stir constantly until it has created a thick sauce. Add the Parmesan and stir to combine thoroughly.
When ready to serve, heat the spinach and then pour the warm cream sauce over the spinach and stir to combine. Serve immediately.