1 sprig fresh rosemary, leaves picked and finely chopped
Zest of 1 lemon
Four 6-ounce amberjack steaks (or other bluefish, such as swordfish or mackerel)
Grapeseed oil, for the grates
For the brine: Whisk the sugar and salt into the warm water and stir until all the granules have dissolved. Let cool prior to using.
For the rub: Using a mortar and pestle, grind the fennel fronds, olive oil, pepper flakes, salt, garlic, rosemary, and lemon zest into a paste.
For the fish: Place the amberjack steaks and in enough brine to cover them completely and place in the refrigerator for 40 minutes. For best results, brine in a container where the whole portion is submerged, such as a deep baking dish, large bowl or plastic container.
Meanwhile, heat a charcoal or gas grill to medium-high heat, lightly the oiling grates.
Remove amberjack steaks from the brine and dab dry. Rub the garlic-fennel rub all over the steaks, coating them liberally. Grill the steaks for 2 to 3 minutes per side. Remove from the grill when the texture changes: the steaks will feel firm to the touch and if you pull at an edge with a fork, it should flake easily.