1. 1. Preheat your oven to 350°F (175°C). Grease a 9-inch (22–24 cm) round springform pan and set it aside.

2. 2. In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

3. 3. Add the eggs one at a time, beating well after each addition.

4. 4. In a separate bowl, whisk together the all-purpose flour, vanilla sugar or extract, and salt.

5. 5. Gradually add the dry ingredients to the butter mixture, beating until just combined. Be careful not to overmix.

6. 6. Pour the batter into the prepared springform pan and spread it evenly.

7. 7. Arrange the rhubarb pieces on top of the batter, leaving a small border around the edges. Sprinkle the raspberries over the rhubarb.

8. 8. Bake for 30-35 minutes, or until the cake is golden brown and a toothpick inserted into the center comes out clean. The fruit should be tender and slightly caramelized.

9. 9. Remove the cake from the oven and let it cool in the pan for about 10 minutes. Then, carefully remove the sides of the springform pan and let the cake cool completely on a wire rack.

10. 10. Once cooled, dust the cake with powdered sugar and serve with lightly whipped cream or a scoop of vanilla ice cream, if desired. Enjoy your delightful Raspberry Rhubarb Clumpy Cake!