Bring a large pot of salted water over medium-high heat to a boil. Add spinach and blanch until bright green and tender.
2
Drain spinach
Remove spinach to a bowl of ice water to stop the cooking process. Drain, then squeeze out excess water.
3
Sauté onions
Heat a large sauté pan over med heat, add olive oil and heat. Add onion and sauté until tender and opaque, about 4 min. Add the garlic and sauté until fragrant.
4
Make the roux
Add the butter and allow to melt then stir in the flour and let the roux cook for a minute until a pale golden brown. Add the milk and cream, whisking to incorporate.
5
Make mornay sauce
Bring the mixture to a simmer, then lower the heat to medium-low, whisking until the sauce thickens, about 5 min. Stir in the Parmesan and cayenne.
6
Add spinach
– Add the spinach, stirring to coat it in the mornay sauce. Serve hot as a side with steak, chicken or fish.