01 -
In a microwave, melt butter and chocolate; stir until smooth. Set aside to cool. In a large bowl, whisk together eggs, milk, vanilla, and the cooled chocolate mixture. Combine flour, sugar, and salt; gradually add to the egg mixture and mix well. Cover the batter and refrigerate for at least 2 hours or overnight.
02 -
In a microwave, melt white baking chocolate with heavy cream; stir until smooth. Let cool. In a small bowl, mix sugar and cream of tartar. Place egg whites in a double boiler or metal bowl over simmering water and stir in the sugar mixture. Constantly whisk until the mixture reaches 120-130°C. Remove from heat and beat on high speed in a mixer with the whisk attachment for 5 minutes. Reduce speed and beat for another 5 minutes until cool and stiff. Transfer to a large bowl. Beat softened butter and vanilla in the same mixing bowl until light and fluffy. Beat in the cooled white chocolate mixture. Gently fold in the meringue in portions until fully incorporated. Cover and refrigerate.
03 -
Heat a lightly greased 8-inch nonstick skillet over medium heat. Pour 2 tablespoons of the crepe batter into the center of the skillet, then lift and tilt to spread evenly. Cook until the top appears dry, about 2 minutes, then flip and cook for another 15-20 seconds. Transfer to a wire rack. Repeat with the remaining batter, greasing the skillet as needed. Stack cooked crepes with waxed paper or paper towels in between.
04 -
Place one crepe on a cake plate and spread with 3 tablespoons of white chocolate buttercream. Repeat the layering process until 10 crepes are used, then refrigerate for 15 minutes. Continue layering and chilling until 30 crepes are stacked, finishing with a crepe on top. Save any remaining crepes for another use. Refrigerate the assembled cake.
05 -
Place chopped semisweet chocolate in a small bowl. In a small saucepan, bring heavy cream, corn syrup, and salt to a boil. Pour over the chocolate and whisk until smooth. Cool, stirring occasionally, until the ganache reaches a spreadable consistency. Spread it over the top and sides of the cake. Refrigerate for 1 hour before serving.