Prepare a regular muffin pan by lining with jumbo muffins liners (see notes how to DIY them from parchment paper).
Coat the blackberries with 1 teaspoon flour in a separate bowl.
1 cup blackberries, 1 teaspoon all purpose flour
In a large bowl whisk to combine eggs, sugar, butter, oil, lemon juice, buttermilk, salt, and vanilla extract.
2 large eggs, ½ cup granulated sugar, ¼ cup butter, ¼ cup vegetable oil, 1 tablespoon lemon juice, ¾ cup buttermilk, ¼ teaspoon sea salt, 1 teaspoon vanilla extract
Sift flour and baking powder on top and fold just until dry streaks of flour disappear.
2 ¼ cup all purpose flour, 2 teaspoon baking powder
Gently fold in the blackberries and immediately scoop the batter into prepared muffin pan, filling ¾ of the way full. Top evenly with the crumble mixture.
Bake at 195°C (385°F) for 18-22 minutes, or until the tops are golden brown and a toothpick inserted through the centre comes out clean.