Blanch the broccoli by placing fresh florets in a large saucepan with about 1 cup of water. Cover and heat on medium-high until simmering. Cook for 4-5 minutes until bright green and crisp-tender, then drain and keep warm in a covered bowl.

Prepare the cheese sauce base by melting 2 tablespoons of butter over medium-low heat in the same saucepan. Stir continuously, then whisk in 2 tablespoons of flour until golden brown, about 1 minute.

Create the creamy cheese sauce by slowly pouring in 1 cup of milk while whisking to avoid lumps. Increase heat slightly and simmer gently for about 3 minutes until thickened.

Add the cheese and seasonings by lowering the heat and gradually stirring in 1 cup of shredded cheddar cheese, followed by ½ cup of grated Parmesan, kosher salt to taste, and optional ingredients.

Combine and serve by pouring the cheese sauce over the warm broccoli or tossing together. Serve warm alongside main dishes.