Place the dough in a buttered bowl, cover with plastic wrap or a clean towel, and leave to rise in a warm place until doubled in size (this will take about 1 1/2 - 2 hour, depending on the warmth of your room). Once it has doubled in size, punch the dough down and, on a lightly floured surface, roll or press into a 13 x 9 inch (33 x 23 cm) rectangle. Transfer to a buttered or parchment lined baking sheet. Then, in a small bowl, whisk together the cream, egg and cinnamon for the egg wash. With a pastry brush, lightly brush the surface of the dough with the egg wash. Cover the dough and let rise until doubled in size (about 45 minutes to 1 hour). 

While the dough is rising, make the streusel topping. In a small bowl combine the sugar, flour, and cinnamon. With a pastry blender, or your fingertips, cut in the butter until the mixture is lumpy. Set aside.

Preheat the oven to 350 degrees F (177 degrees C) and place rack in center of oven. When the dough has doubled in size, once again lightly brush the surface of the dough with the egg wash. Evenly place the blackberries and diced apple on the dough and then sprinkle with the streusel topping. Bake for about 35 minutes or until nicely browned and cooked through. Remove from oven and place on a wire rack. Serve warm or at room temperature.

Serves 6 - 8