How to cook
Clean the blueberries and drain them of the excess fluid. Mix the flour, sugar, salt and baking powder in a bowl. Separately, mix the oil, eggs and milk and stir until homogenized. Add the wet mixture to the dry and mix it well. Finally mix with the blackberries.
Optionally, you can add a few chopped nuts. Divide up the mixture into 12 greased muffin molds.
Mix together the cinnamon, butter, 1/4 cup flour and 1/3 cup brown sugar into a crumbly mixture. Spread it on the cupcakes and put them to bake in a preheated 356°F (180 °C) oven for about 25 minutes.