Heat oven to 180°C / 350° F / Gas 4.

Grease the sides and line the base of an approximately 29 x 18cm deep sided baking dish. Cut a piece of baking paper to the size of the base of the dish, lay that inside and grease the paper too.

Sprinkle the brown sugar evenly over the baking paper, then lay the plums on top in one layer, with the skin facing down.

In the bowl of a stand mixer, or using an electric hand mixer, beat together the butter, caster sugar, vanilla essence, nutmeg and ginger until pale and creamy. Scrape down the sides of the bowl, then beat in the eggs, one by one, ensuring each is well mixed in before adding the next.

In a separate bowl, whisk together the ground hazelnuts, flour and baking powder, then add to the creamed butter and sugar, mixing on a the lowest speed, just until combined. Stir once or twice with a big spoon to make sure that everything is mixed in, then spoon the mixture over the plums, smoothing the top so that it is nice and even.

Bake in the bottom third of the preheated oven for 50 minutes, until golden brown on top and a skewer inserted into the middle of the cake comes out clean. Allow to rest in the dish for 10 minutes before loosening the sides with a knife and turning out onto a serving plate or board.

Allow to cool to room temperature before cutting and serving.