Preheat the oven to 425 degrees F (218 degrees C).

Boil a large pot of water with 2 teaspoons of sea salt. Add the brussels sprouts and boil for 8-10 minutes until tender. Run under cold water or plunge into an ice bath to prevent overcooking. Drain and pat dry with a paper towel.

In a large bowl, toss the brussels sprouts with olive oil, garlic powder, remaining 1/2 teaspoon of sea salt, and cayenne pepper. Add 5 tablespoons of parmesan cheese (if using) and toss again.

Spray a baking sheet with cooking spray or brush with oil. Arrange the sprouts in a single layer with about 1.5-2 inches of space between them.

Using the bottom of a glass or mason jar, push down on the sprouts to smash them flat. Sprinkle the remaining 3 tablespoons of grated parmesan cheese on top (optional).

Roast smashed brussels sprouts for 25-30 minutes, flipping halfway through, until golden and crispy on both sides.