Preheat the oven to 200°C.
Grease and line a 25cm x 35cm roulade tin with greaseproof paper.
Whisk eggs and sugar in a large bowl until pale and thickened.
Stir in melted butter, then sift in cocoa powder and flour.
Pour mixture into the tin and bake for 10 to 12 minutes.
Turn cake onto a tea towel scattered with hazelnuts and cool for 5 minutes.
Spread a mixture of whipped cream and hazelnuts over the cake and roll tightly.
Melt chocolate and cream together over a pan of simmering water to make a sauce.
Pour sauce over the roulade and decorate with sliced strawberries.