In a bowl placed over a pot of simmering water or in a microwave oven, melt the white chocolate with 1/2 cup (125 ml) of the cream. Remove from the heat. Add the remaining cream (1 1/2 cups/375 ml) and the lemon zest. Stir well.
Cover and refrigerate for about 3 hours or until the cream
Meanwhile, in a bowl, combine the flour, sugar, baking powder and salt. Add the eggs, 1 cup (250 ml) of the milk and the vanilla. Stir with a whisk until smooth. Gradually stir in the remaining milk (1 1/4 cups/310 ml).
In an 8-inch (20 cm) non-stick skillet brushed with butter over medium heat, cook the crepes, one at a time, using about 1/4 cup (60 ml) of batter per crepe. Cook until golden brown on both sides. Place the crepes on a baking sheet lined with parchment paper as you go, until you have 16 crepes. Cover with plastic wrap and let cool completely.
Beat the white chocolate mixture and mascarpone with an electric mixer until stiff peaks form.
On a serving plate, place 1 crepe. With a spatula, spread the crepe with 1/3 cup of the white chocolate mascarpone cream. Cover with another crepe and spread with 1/3 cup of the cream. Repeat the sequence with the remaining ingredients to create 12 to 14 layers of crepes, using a crepe as the top layer. Refrigerate for 30 minutes before serving.
When ready to serve, dust with icing sugar. Serve with Raspberry Sauce (see recipe). The Mille Crepe Cake will keep for 1 day in the refrigerator.
Using two skillets to prepare the crepes will cut down on your preparation time.
The crepes may be made the day before assembling the cake.