Whisk all the ingredients until the dough is smooth. Mix in the blackberries carefully.
Grease the baking dish with oil and sprinkle with flour. Pour in the dough.
Bake for about 20 minutes at 400 ° F.
Spread the lemon icing over the cooled pie.
Put sugar and lemon juice in a bowl and pour hot water over it. Stir well until a smooth icing is formed.