In a food processor, puree the liver. Add the egg and pulse to combine. (Do not run at high speed or it will get frothy.) Over medium heat combine the cream, milk, kombu, dried shiitakes, soy sauce, and spices and bring the mixture to a boil. Remove from the heat. Combine the egg/liver puree with the cream mixture and pass through a fine chinoise. Pour the custard into caramel-lined ramekins.
Place the ramekins into a bain marie, cover with foil, and bake at 325 degrees F for about 10 to 12 minutes (the middle should be wobbly). Remove from the bain marie and allow to cool to room temperature.
Place the grapes, olive oil, cinnamon, bay, rosemary, salt, and pepper in a saute pan and place over medium-high heat. Cook, stirring occasionally, until the grapes brown and blister. Add the vinegar and the maple syrup and remove from the heat. Allow to cool to room temperature.
To unmold the creme caramels, give them a little jiggle back and forth to loosen them within the ramekin. Place a plate over the top of the ramekin and flip it over, allowing the creme caramel to fall onto the plate. Add a little bit of flourish (and herbaceous goodness) with a few watercress sprigs and drizzle with truffle oil, and spoon some grapes around the mousse. Place a crispy piece of pancetta next to the creme caramel and serve with the toasted brioche.
Recipe courtesy of Brad Farmerie, Executive Chef of Public in New York City, for Grapes from California