Bring a large pot of salted water to a boil and cook the elbow macaroni according to the package instructions, stopping about 2 minutes before it's fully cooked. During the last 2 minutes of boiling, add the broccoli florets to the pot. Drain everything and set aside.

Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish and set aside.

While the pasta is cooking, melt the butter over medium heat in a medium saucepan. Once it’s melted, whisk in the flour and cook for 1-2 minutes until it forms a smooth paste. Stir in the garlic powder until fully combined.

Gradually add the milk, starting with a small amount and whisking constantly to avoid lumps. Stir continuously until all the milk is incorporated and the sauce thickens.

Next, stir in the Dijon mustard, nutmeg, salt and black pepper.

Remove the saucepan from the heat and mix in most of the Gruyere and cheddar cheeses, reserving some for topping. Stirring until the cheese is fully melted and the sauce is smooth.

Add the cooked pasta and broccoli to the cheese sauce and stir until everything is well coated.

Transfer everything into your prepared greased baking dish and spread it out into an even layer.

Sprinkle the remaining cheese and then the Panko breadcrumbs over the top.

Bake the mac and cheese in the preheated oven for 15-20 minutes or until the top is golden brown and the cheese sauce is bubbling around the edges. Let it cool for about 5 minutes before serving.