Bring a large pot of heavily salted (seawater-salty) water to a boil. Blanch the broccoli florets for 3 minutes, then shock them in an ice bath. When chilled, 3 to 4 minutes, drain and transfer the florets to the refrigerator to dry thoroughly, 30 minutes.
Preheat a grill to medium-high heat.
Combine the butter, red pepper flakes and the remaining 1 tablespoon salt in a small saucepot and set over low heat to melt the butter.
Place the lemon halves on the grill, cut-side-down. Grill until lightly charred, then set aside. Grill the broccoli for a minute or two on all sides, until lightly charred and warmed through. Squeeze the juice of 4 lemon halves over the broccoli during grilling. Toss the broccoli and butter together in a bowl and serve, garnished with the remaining grilled lemon halves.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.