Pour water to a depth of about 2 inches into a saucepan or the bottom pan of a double boiler and bring to a bare simmer. In a large stainless steel or other heatproof bowl or the top pan of the double boiler, whisk together the egg yolks, honey and Marsala until well blended. Set the bowl or pan over, but not touching, the simmering water and whisk vigorously until the mixture lightens in color and thickens and the whisk leaves a trail, about 3 to 5 minutes. To test, draw the whisk through the center of the mixture; it should leave a clean trail on the bottom of the bowl or pan. Add the wine and continue whisking constantly until the mixture is pale, thick, and greatly expanded in volume, about 10 minutes. Do not let the mixture boil or the eggs will curdle. When the zabaglione is light and fluffy and holding a soft peak, remove from the heat and let cool at room temperature for 10 minutes, whisking occasionally.
Meanwhile preheat the oven to 425 degrees F.
Add the biscotti to a 10-inch gratin dish. In a small bowl, combine the raspberries, lemon juice, and salt and toss lightly. Arrange the berries over the biscotti. With a large spoon, scoop the zabaglione over the raspberries, and sift the sugar over the top. Arrange the gratin dish on a baking sheet and place in the oven. Bake the gratin until the tops are golden brown in spots about 10 to 12 minutes. Remove from the oven, let rest for 5 minutes and serve warm.