1. Preheat the oven to 210oC fan and line a 12 hole muffin tin with muffin cases.
2. Mix together the flour, baking powder, bicarbonate of soda and cinnamon in a large bowl. Combine the melted butter, sugar, eggs and milk in a separate jug, then add to the dry ingredients and mix briefly to combine. Add the blackberries.
3. In a separate small bowl, stir together the sugar, flour, melted butter and espresso powder until it looks crumbly. Divide the muffin batter between each hole, then sprinkle the crumble mix on top.
4. Bake at 210oC fan for 5 minutes, then reduce the temperature to 190oC fan for a further 10-12 minutes. Enjoy warm, or leave to cool.