Heat oven to 450°F and set a large, rimmed sheet pan on the middle rack in the oven while it heats.

Bring a large pot of water and 1 teaspoon salt to boil. Rinse and cut the broccoli into florets, ensuring they are all about the same size.

Fill a large mixing bowl with ice water and set it next to the stove.

When the water is boiling, add the broccoli florets and set the heat to medium-low. Boil the broccoli for 2 minutes.

After 2 minutes, use a slotted spoon to submerge the broccoli in the ice water for 2 minutes.

Transfer the broccoli to a paper towel-lined plate to dry and pat dry with another paper towel.

In a large bowl, mix together the broccoli, olive oil, 1 teaspoon salt, and black pepper.

Remove the hot baking sheet from the oven and spread the broccoli mixture evenly over the pan.

Set the oven to broil and return the pan with the broccoli to the middle rack of the oven. Broil the broccoli for 4 minutes.

While the broccoli is broiling, in a medium bowl, mix together the melted butter, panko crumbs, shredded cheddar, grated Parmesan cheese, and red pepper flakes.

Remove the pan from the oven and sprinkle the breadcrumb/cheese mixture evenly over the top of the broccoli.

Return the broccoli to the oven and broil for another 3-5 minutes or until the broccoli is fork-tender and the cheese has melted and is crispy around the edges. Watch closely to prevent burning.

Serve immediately.