Makes 10 servings
For the terrine:
Cook the cauliflower in boiling, salted water for about 10 minutes. Remove the cauliflower and drain. In the same water, cook the broccoli for 5 minutes, and drain.
Melt the butter in a large skillet, add chopped onion, and saute over medium heat for 5 minutes.
In a food processor, puree the cauliflower with half the onions, 2 of the eggs, the cheese, 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper. Transfer the cauliflower mixture to a bowl. In the same manner, puree the broccoli with the remaining onions, eggs, salt, and pepper, adding the bread crumbs and parsley also.
Butter a 9-by-5-inch loaf pan well, then line it with a strip of aluminum foil as wide as the pan and long enough to come part way up the sides. Butter the foil also.
Fill the pan with alternating large spoonfuls of the two vegetable purees, then run a knife through the mixture a few times to marble it slightly. Cover with a piece of buttered wax paper. Place pan in a larger baking pan holding enough hot water to come halfway up its sides, and bake in a 350-degree oven for 55 to 65 minutes, or until a cake tester inserted in the center comes out fairly clean.
If you are serving the terrine immediately, let it cool about 15 minutes, then run a knife around the inside of the pan, peel off the wax paper on top, place a platter or cutting board over the ban, and invert the terrine onto it carefully. Remove the pan and foil. If you prefer make the terrine a day ahead and refrigerate it, after cooling, in its pan. Then reheat it, covered, in a 325-degree oven for 30 minutes, and follow the instructions for unmolding.
To make the red-pepper sauce:
Cut the peppers in half and discard the seeds and stems. Place the halves cut sides down on a baking sheet and roast under a hot broiler until they are black and blistered. Let them steam in a closed paper bag for a few minutes, then remove the charred skin. Place the peppers in a food processor with the other ingredients and process until smooth. The sauce should be thick, but if it is too thick to pour, add a little more vinegar and or a little water. Taste for seasoning. Serve warm.
To serve, cut the terrine into 3/4-inch-thick slices with the aid of a spatula and place each slice on a plate in a pool of warm red-pepper sauce.