Preheat the oven to 375 degrees and lightly grease a 9x13 baking dish. Bring a large pot of salted water to a boil.

Cook the pasta shells according to package directions until just al dente. Drain and set aside.

In the same pot or a steamer basket, cook the broccoli florets for 3 minutes until bright green and crisp-tender. Drain and set aside with the pasta.

In a medium saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1 minute until bubbly.

Slowly pour in the milk while whisking. Continue cooking and stirring until the sauce thickens, about 3 to 4 minutes.

Remove the sauce from heat and stir in 1 1/2 cups of the cheddar cheese along with the salt and pepper until smooth.

Add the drained pasta and broccoli to the sauce and stir gently to coat everything evenly.

Transfer the mixture to the prepared baking dish. Sprinkle the remaining 1/2 cup cheddar cheese over the top.

Bake for 15 to 20 minutes until the cheese is melted and the edges are lightly golden. Let it rest for 5 minutes before serving.