Begin by placing the fresh broccoli florets in a large saucepan and adding about 1 cup of water. Cover the saucepan with a lid and bring the water to a gentle simmer over medium heat. Steam the broccoli for 4-5 minutes, until it turns bright green and is crisp-tender. Once done, drain the broccoli and set it aside while you prepare the cheese sauce.

In the same saucepan, melt 2 tablespoons of butter over medium-low heat, swirling it until fully melted. Once bubbling, whisk in 2 tablespoons of flour and continue whisking for about 1 minute, until it becomes golden brown.

Gradually pour in 1 cup of milk while continuously whisking to prevent any lumps from forming. Increase the heat slightly and let the mixture come to a gentle simmer. Continue simmering for about 3 minutes, whisking often, until the sauce thickens and coats the back of a spoon.

Reduce the heat to low and slowly stir in ⅔ cup of shredded cheddar cheese and 2 tablespoons of grated Parmesan cheese, allowing each addition to melt completely before adding more.

Mix in ¼ teaspoon of kosher salt, along with a pinch of ground mustard and cayenne, if using. Taste your cheese sauce and adjust the seasoning as needed.

Once everything is perfectly combined, reintroduce the steamed broccoli to the saucepan and gently stir it into the warm cheese sauce. Serve the Cheesy Broccoli warm as a delightful side dish.