Ingredients

· ¾ cup unsalted butter, plus more for pan

· 1lb. ripe plums, coarsely chopped

· 6oz. bittersweet chocolate (70–72% cacao), coarsely chopped

· 5 large eggs, room temperature

· 1½ cups sugar

· ¾ cup all-purpose flour

· 1tbsp baking powder

· ¼ tsp salt

· 1½ cups cold heavy cream

· Unsweetened cocoa powder (for dusting)

Method

Preheat oven to 170°C. Butter bottom and sides of a 9-inch springform pan and line bottom with parchment paper. Purée plums in a blender until very smooth (you need 1½ cups, reserve any additional purée for another use). If plums are not ripe enough to form a very smooth purée, strain through a fine-mesh sieve. Combine chocolate and butter in a large heatproof bowl then set it over a medium saucepan of barely simmering water (do not let bowl touch water). Stir until chocolate is melted and smooth then remove from saucepan. Stir plum purée into chocolate mixture until well combined. Using an electric mixer on medium speed, beat eggs and sugar in another large bowl until pale and tripled in volume, for 10-12 minutes. Using a rubber spatula, fold about 1/3 of the egg mixture into chocolate mixture to lighten, then fold chocolate mixture into remaining egg mixture until combined. Combine flour, baking powder and salt in a medium bowl then fold dry ingredients into chocolate mixture until combined. Pour batter into prepared pan and smoothen the surface. Bake cake until centre is set and sides are beginning to brown, for 45-55 minutes. Transfer to a wire rack and let the cake cool completely in pan. Meanwhile, using an electric mixer on medium-low speed, beat cream in a large bowl until soft peaks form. Unmold cake and transfer to a platter. Mound whipped cream on top of the cake then dust with cocoa powder.