01 - Preheat the oven to 375°F. Grease a medium baking dish.
02 - Boil elbow 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 to form a roux.
04 - Gradually whisk in milk and cook, stirring constantly, until sauce thickens, about 5 minutes. Lower heat to medium-low, then add cheddar and Gruyère cheeses. Stir until melted and smooth. Incorporate Dijon mustard, ground nutmeg, salt, and pepper.
05 - Stir fresh spinach into the hot cheese sauce until wilted.
06 - Mix drained macaroni into the cheese and spinach sauce until thoroughly combined. Transfer mixture to the prepared baking dish.
07 - In a small bowl, blend panko breadcrumbs, grated Parmesan, and olive oil. Evenly sprinkle over the macaroni mixture.
08 - Bake in the preheated oven for 20 to 25 minutes or until the topping is golden and sauce bubbles.
09 - Allow to cool for 5 minutes before serving.