To make the sweet ginger-soy sauce, in a small microwave-safe bowl or cup, combine the soy sauce and mirin and microwave on full power for about 1 minute, or until the mixture comes to a boil. Or, combine the soy sauce and mirin in a small saucepan, bring to a boil over high heat, and remove from the heat. Stir in the ginger, let cool, cover, and refrigerate until serving or up 4 days. You should have 8 teaspoons.
To serve, place a piece of tofu in each of 16 ceramic Chinese soupspoons. Put about 1 teaspoon smoked salmon on top of each tofu piece, and top the salmon with 1/4 teaspoon scallion. (The dish can be prepared to this point up to 4 hours in advance, tightly covered, and refrigerated.) Finish each spoon with 1/4 teaspoon salmon roe, and garnish with 1 chervil leaf.
Carefully pour 1/2 teaspoon sweet ginger-soy sauce into the bowl of each spoon, so it surrounds the tofu. (Do not spoon it over the tofu.) Place the spoons on a serving tray, and encourage your guests to enjoy the tofu directly from the spoon.
Photos from the Great Gatherings: Star Chefs Entertain at Home Cookbook