Step 1

Line a 1L loaf pan with plastic wrap, leaving plenty overhanging the sides.

Step 2

Whiz the berries in a food processor or blender to a puree. Pass through a sieve, pressing down to extract as much juice as possible and discarding the solids.

Step 3

Whisk eggwhites in an electric mixer until frothy, then add sugar, 1 tablespoon at a time, whisking until thick and glossy.

Step 4

Whisk cream and vanilla with electric beaters to stiff peaks. Fold the cream into the eggwhite mixture, then swirl through the raspberry puree. Pour into the pan, cover with overhanging plastic wrap and freeze overnight until firm.

Step 5

The next day, place the chocolate in a heatproof bowl set over a pan of gently simmering water, stirring until melted and smooth. Lay the transfer sheet, if using, or a 40cm x 25cm sheet of baking paper on a clean work surface and pour the chocolate over the top. Spread evenly over the whole sheet with a palette knife, then chill until set.

Step 6

Once set, cut the chocolate into 24 small rectangles, then carefully peel off transfer sheet plastic or baking paper. Scoop the parfait onto 6 serving dishes, then use the chocolate rectangles to form a box around the parfait. Garnish with raspberries and serve.