Upside-down plum & hazelnut cake

Preheat the oven to 180ºC, gas mark 4; grease and line the base and sides of an 18cm round, deep cake tin with baking parchment. Mix together the demerara sugar and cornfour in a small bowl and scatter over the base of the tin, then dot over the butter. Place the plum halves in one flat layer in the tin, some facing up and some down. Scatter the halved hazelnuts around the plums; set aside.

For the cake batter, put the hazelnuts in a food processor and whizz to a rough crumb. Add the rest of the batter ingredients with a pinch of salt, then whizz until well combined. Spoon the mixture on top of the plums in the tin and spread evenly. Bake in the centre of the oven for 20 minutes. Rotate the cake in the oven for an even bake and bake for a further 10-12 minutes until springy to touch (the skewer test won’t work here because of the soft plums on the base). Leave to cool for 10 minutes before turning out onto a serving platter and serve with a dollop of crème fraîche, if liked. The cake will keep well for up to 3 days in an airtight container.