Preheat the oven to 375° F. Line a muffin tin with paper liners and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, cinnamon, and salt. Set aside.
In a separate bowl or glass measuring cup, combine the buttermilk, melted butter, oil, eggs, and vanilla. Pour the wet ingredients into the dry and mix until just combined, being careful not to overmix.
If your blackberries are big, you can cut them in half or into quarters. Toss the blackberries in a spoonful of flour, mixing until well coated. This helps them from sinking in our muffins. Pour them into the batter and gently fold them in.
Scoop the batter into the muffin tin, filling about ¾ of the way full. Top with coarse sugar (or streusel if you made some). Bake for 17-23 minutes, or until a toothpick inserted comes out clean. Allow the muffins to cool in the pan for 5-10 minutes before transferring them to a wire cooling rack to cool completely.
Video
Notes
Use a good quality muffin tin- this one is my favorite!