Preheat oven to 350F degrees.
In a large bowl, whisk the flour, baking soda, baking powder, cinnamon and salt.
In a separate bowl, whisk the buttermilk, sugar, eggs, oil, lemon juice and vanilla.
Stir the wet ingredients into the dry ingredients until well combined.
Slice the blackberries in half and fold them into the batter.
Make the crumb topping: In a small bowl, whisk the flour and both sugars. Stir in the melted butter using a fork, until the mixture is crumbly.
Coat two muffin pans with nonstick cooking spray, or line with cupcake liners. Fill each muffin cup 2/3 of the way full of batter. Sprinkle the crumb mixture generously over top.
Bake 35 minutes, until a toothpick inserted in the center comes clean. Cool in the muffin pan for at least 20 minutes before removing.