Start by placing fresh broccoli florets in a large saucepan with about 1 cup of water. Cover the pan and bring it to a gentle simmer over medium heat. Steam the broccoli for 4 to 5 minutes, until it turns bright green and is crisp-tender. Once cooked, drain the broccoli and set it aside, ready to be smothered in the delicious cheese sauce.

In the same saucepan, melt 2 tablespoons of butter over medium-low heat. Once melted, sprinkle in 2 tablespoons of flour, whisking continuously for about 1 minute until the mixture turns a golden brown.

Gradually whisk in 1 cup of milk, stirring gently to avoid lumps. Continue to cook the mixture on medium-low heat, allowing it to thicken, which should take about 3 minutes.

Once the milk mixture has thickened, slowly stir in 1 cup of shredded cheddar cheese and 1/4 cup of grated Parmesan cheese. Mix constantly until both cheeses melt completely, creating a luscious, creamy sauce.

Add in 1/2 teaspoon of kosher salt, along with optional ground mustard and cayenne pepper, to taste. Stir thoroughly to infuse the flavors.

Combine the steamed broccoli with the cheese sauce in the saucepan. Gently mix until the broccoli is fully coated in the creamy goodness.