Blackberry Roly-poly

Steps

1. Cook the blackberries in the water and 1/4 teaspoon salt until the berries are soft.
2. Rub the berries through a sieve. Add the 240 ml sugar to the pulp.
3. Return the mixture to the heat and cook until it thickens, stirring occasionally.
4. Sift the flour with the baking powder and 1/2 teaspoon salt.
5. Work in the Cottolene with the tips of your fingers.
6. Mix the egg yolk with 1/470 ml milk, then mix into the flour mixture to form a soft dough.
7. Turn the dough onto a floured board and knead slightly.
8. Roll the dough into a rectangular sheet 1/4 inch thick.
9. Divide the sheet into four pieces, longer than wide.
10. Spread each piece with the blackberry sauce, reserving some sauce to serve.
11. Roll up each piece like a jelly roll. Wet the edges and press lightly to prevent unrolling.
12. Lay the rolls on a buttered baking sheet.
13. Brush the tops with the slightly beaten egg white. Sprinkle with granulated sugar and a few grains of ground cloves.
14. Bake for 25 minutes in a hot oven.
15. Serve hot with the remaining sauce, kept hot over hot water.