01 - Preheat oven to 375°F. Lightly grease a medium baking dish.
02 - Boil macaroni in a large pot of salted water until al dente. Drain and set aside.
03 - Melt butter in a saucepan over medium heat. Whisk in flour and cook for 1 to 2 minutes.
04 - Gradually whisk in milk. Stir constantly until sauce thickens, about 5 minutes.
05 - Reduce heat to medium-low. Stir in cheddar and Gruyère until smooth. Mix in Dijon mustard, nutmeg, salt, and pepper.
06 - Fold fresh spinach into the sauce and cook until wilted.
07 - Mix drained macaroni with cheese and spinach sauce. Transfer mixture to prepared baking dish.
08 - Combine panko, Parmesan, and olive oil in a small bowl. Spread evenly over macaroni.
09 - Bake for 20 to 25 minutes until topping is golden and sauce bubbles.
10 - Allow to cool for 5 minutes before serving.