Plum and Blueberry Crumb Cake

Ingredients (for a 22-cm-diameter springform pan)
For the hazelnut crumb topping
70 g of Soft wheat flour type 1
30 g of chopped hazelnuts
50 g of brown sugar
55 g of butter
1/2 level teaspoon ground cinnamon
1 pinch of salt

For the crust
200 g of Soft wheat flour type 1
120 g of softened butter
125 g of granulated sugar
3 medium eggs at room temperature
100 g of full-fat Greek yogurt at room temperature
7 g of baking powder
1 teaspoon vanilla extract
1 pinch of salt

For the fruit
400 g of ripe but still firm plums, net weight
100 g of fresh blueberries

Procedure
For the hazelnut crumb topping
To begin, melt the butter and let it cool slightly. In a bowl, combine the flour, chopped hazelnuts, brown sugar, cinnamon, and salt, and mix with a fork. Then pour in the melted butter and mix until the ingredients are evenly moistened. Finally, place the mixture in the refrigerator: as it cools, the butter will firm up, allowing you to form the large, irregular crumbs typical of a crumb topping. Meanwhile, butter a 22-cm springform pan and line the bottom with parchment paper, then preheat the conventional oven to 175°C.
Now wash the plums and blueberries and dry them thoroughly. Cut the plums in half, remove the pits, and cut them into wedges about 1–1.5 cm wide at their widest point. Set the fruit aside without seasoning it.

For the base
In a bowl, cream the softened butter with the sugar using an electric mixer for about 3–4 minutes until the mixture is light in color, creamy, and well aerated. Add the eggs one at a time, waiting until each is fully incorporated before adding the next: if the mixture tends to separate during this step, add 1–2 tablespoons of the flour called for in the recipe and mix briefly. Finally, add the vanilla extract. Now sift the flour with the baking powder and add the salt, then fold the dry ingredients into the previous mixture, alternating them with the Greek yogurt. Mix everything on low speed just long enough to achieve a smooth batter. Once the flour has been added, transfer the dough to the pan and level it with a spatula, then arrange the plum wedges evenly and fairly densely over the surface, without pressing them into the dough. Fill in the remaining spaces with blueberries. Now take portions of the crumble mixture with your fingers, press them together lightly, and break them over the fruit, forming irregular crumbs of varying sizes. Spread them over the entire surface without pressing them down, allowing some of the fruit to peek through here and there.

Bake the crumb cake in a preheated conventional oven at 175°C for about 65–75 minutes, checking for doneness starting at the 50-minute mark. If the crumb topping begins to brown too much before the cake is done in the center, gently cover the top with a sheet of aluminum foil and continue baking. Test for doneness by inserting a toothpick into the fruit: it should come out dry or with just a few moist crumbs, but with no traces of raw batter. Remove the crumb cake from the oven and let it cool slightly in the pan for about 30 minutes, then remove the ring and let it cool completely before transferring it to a serving plate and slicing it.

In collaboration with Fiordifrolla