Make the pastry cream: In a 1-quart pot, bring the milk and lemon zest to just below the boiling point; remove from the heat. In a medium bowl, beat the egg, egg yolks, and sugar until creamy. Add the flour and vanilla as you beat with a whisk, then slowly beat in the hot milk, still whisking. Pour the mixture into the pot in which you heated the milk. Cook over medium heat, stirring, until thick, about 5 minutes. Transfer to a bowl, cover, and refrigerate 2 hours.

Make the chocolate sauce: Melt the chocolate, cocoa, and ¼ cup water in a bowl set over a pot of simmering water, stirring until melted. Remove from the heat, still stirring, then add the sugar. Return to the heat and stir until the sugar dissolves, about 3 minutes, stirring constantly. Add the cream and stir until smooth. Remove from the heat; cool 5 minutes.

To layer: Line an 8" square serving dish with 12 of the ladyfingers, drizzle with ¼ cup Vin Santo, and top with one-quarter of the pastry cream. Drizzle with half of the chocolate sauce and top with another quarter of the pastry cream. Make a second layer in the same manner. Refrigerate 2 hours and serve chilled, garnished with the raspberries.