- Ganache filling:
- 14 oz dark chocolate chips
- 1 3/4 cups heavy cream
- Wafer roll:
- 1/2 cup icing sugar
- 1/3 cup butter, melted
- 1 tbsp heavy cream
- 1/2 tsp vanilla
- 2 egg whites
- Pinch salt
- 1/2 cup flour
- 1 tsp cocoa powder
- Make the ganache filling: Warm the cream, and pour over the chocolate chips. Let stand for 1 minute, then slowly whisk together. Chill for 30 minutes. Use an electric whisk to whip until light and fluffy. Pour out onto plastic wrap and form into a sausage, the same length as your pan. Put in the fridge for 2 hours.
- Make the wafer roll: Preheat the oven to 375 degrees. Line a Swiss roll pan with baking paper.
- In a large bowl, mix together the icing sugar, melted butter, heavy cream and vanilla. Using an electric hand whisk, mix in the egg whites until the mixture is light and fluffy. Add the flour and salt and fold through until just mixed.
- Put three tablespoons of the mixture into a separate bowl and stir in the cocoa powder. Transfer to a piping bag and cut a small hole in the end.
- Spread the plain mixture across the baking sheet, then pipe diagonal chocolate lines across the whole sheet. Just before you put it in the oven, unwrap the ganache sausage, and trim the ends flat.
- Bake the wafer for 5 to 6 minutes. Watch it carefully and take it out of the oven when the edges are brown and the top is just starting to color. Flip the wafer out onto a clean work surface. Start to roll the long edge nearest you around a rolling pin to create the start of the round shape, then swap the rolling pin for the ganache sausage and roll up like a cigar. Allow it to set for 5 minutes, seam side down, before slicing and serving.