For the blackberries:
Brown sugar coating:
Heat the oven to 360°F.
Blend the blackberries with 1/4 cup of sugar and set aside.
Mix all the dry ingredients in a bowl. Separately, mix all the wet ingredients. Then incorporate the wet ingredients in the dry ingredients with a mixer and beat until everything is incorporated.
Transfer half of the mixture to a previously oiled mold, put the blackberries with sugar and then add the remaining mixture.
Combine the ingredients for the sugar coating with a spoon and sprinkle the cubes on the mold until covering it completely.
Bake for 40 minutes or until the sponge cake starts to brown on top.