How to Make It
Light the grill or heat the broiler. In a small stainless-steel saucepan, combine the oil, garlic, sage, and rosemary. Cook over moderately low heat until the garlic just starts to brown, about 2 minutes. Remove from the heat and immediately stir in the vinegar, 1/4 teaspoon of the salt, and the pepper.
Put the trout fillets in a medium glass dish or stainless-steel pan. Sprinkle the fish with the remaining 1/4 teaspoon salt. Add half of the oil-and-vinegar mixture and turn to coat. Grill or broil the fish skin-side down for 2 minutes. Turn and cook until just done, about 2 minutes longer for 1/4-inch-thick fillets. To serve,whisk the remaining oil-and-vinegar mixture and pour it over the hot fish.
Fish Alternatives In place of the trout, try relatively firm fillets, such as Arctic char or salmon. Whole fresh sardines, if you can find them, would also be delicious.
Test-Kitchen Tip If you don't plan to grill the trout right away, let the oil and vinegar cool completely before adding the mixture to the fish. Otherwise, the hot oil and vinegar will start to cook the fish immediately.