Center a rack in the oven and preheat the oven to 350 degrees F. Line a baking sheet with parchment paper and arrange the sardines or salmon in a single layer on the pan. Season the fillets on both sides with salt and pepper and one quarter of the olive oil. Scatter half the sage, thyme, rosemary, and garlic over the fillets and slide the pan into the oven. Roast the sardines for 7 minutes, or until they're just cooked through. Remove the sardines from the baking pan, cool, and then chill in the refrigerator. Re-line the baking sheet with clean parchment paper and arrange the eggplant on the sheet. Season the eggplant slices with salt and pepper as well as the remaining oil and herbs. Bake the eggplant for 20 to 25 minutes, or until tender. Cool and then transfer to the refrigerator to chill. Line an 8 1/2 by 4 1/2 by 2 1/2-inch loaf pan with plastic wrap, allowing it to extend over the sides. The terrine will be built with the eggplant, peppers, sardines, and tomatoes in layers, starting with the eggplant. To begin, cut the eggplant slices to fit the terrine and lay a layer of eggplant over the bottom and up the sides of the terrine, allow the slices to overlap a little and overhang the edges. Top with peppers, then sardines, then tomatoes. Repeat with the remaining ingredients, finishing by folding the overhanging eggplant over the top of the terrine and leveling the top with an additional layer of eggplant slices. Cover the top with the plastic wrap that's hanging over the sides and press another piece of plastic wrap against the top for good measure. Cut a piece of corrugated cardboard to fit inside the top of the terrine and press it down firmly against the plastic wrap. Place a weight, such as a 1-pound can, on top of the cardboard, put the terrine on a parchment-lined tray (to catch any drips that result from the weighting), and refrigerate for at least 12 hours, or overnight.
To serve: If you have an electric knife, now's the time to use it, if not, choose a long thin serrated knife and work with a sawing motion. Remove the weight, the cardboard, and the sheet of plastic wrap. Carefully cut the loaf into slices, each no less than 1-inch thick (thinner slices will fall apart.) If you'd like, serve the terrine with a small green salad dressed with lemon juice and olive oil.
To drink: A Spanish white Ruede, rich, oaky, and even though it's white, berryish.
Recipe from Daniel Boulud's Cafe Boulud Cookbook, by Daniel Boulud and Dorie Greenspan, published by Scribner, 1999