1. Soak the vegetable strips in a bowl of ice cubes and water for an hour to crisp them. Pat dry with paper towels and arrange on a platter with the romaine leaves, tomatoes and mushrooms. Cover with plastic wrap and refrigerate. Arrange the bread sticks on a separate plate and set aside.
2. In a heavy 1-quart enameled or stainless-steel saucepan, bring the cream to a boil and cook it, stirring frequently, for about 15 to 20 minutes, or until it has thickened and has reduced to about 1 cup.
3. Choose a 3- or 4-cup enameled or flameproof earthenware casserole that fits over a candle warmer, spirit lamp or electric hot tray. On the stove, melt the butter in the casserole over low heat; do not let it brown.
4. Add the anchovies and garlic, then the reduced cream and the optional truffle, and bring the sauce to a simmer, stirring constantly. Do not let it boil.
5. Serve the bagna cauda at once, accompanied by the cold vegetables and the bread sticks. To eat, pick up a vegetable or bread stick with your fingers and dip it into the hot sauce.
6. If the butter and cream separate as the sauce stands, beat with a wire whisk. (You may substitute almost any raw vegetable you like for bagna cauda fennel sticks, cauliflower or broccoli flowerets, white turnip wedges, or red or white radishes.)
