The inspiration for this dish comes from Restaurante Antonio in Zahara de los Atunes, where my family spends the summer.
Technique tip: Don't bother removing the fish scales before baking; it'll take more time and will bruise the flesh of the fish.
Preheat the oven to 400°F. Line a large rimmed baking sheet with foil or parchment paper. In a large bowl, mix the kosher salt with 1/2 cup of water until it resembles moist sand. Strip the leaves from half of the rosemary and thyme sprigs and mix into the bowl along with 2 of the bay leaves.2.
Spread half of the salt mixture in the center of the baking sheet and place the remaining rosemary and thyme sprigs and bay leaves on top. Lay the fish on the mound, then cover with the remaining salt mixture, lightly packing it to completely cover the fish.3.
Bake the fish for about 35 minutes, until an instant-read thermometer inserted into the fish registers 135°F. Remove from the oven and let stand for 5 minutes. (The fish will continue cooking as it stands.)4.
Crack the top salt crust and discard it. Remove and discard the skin from the top of the fish and, using a fish spatula, carefully transfer the top fillet to a platter. Flip the fish over and repeat the process. Drizzle with olive oil and sprinkle with flaky sea salt. Serve.