Preheat the oven to 425°F, 220°C, or gas mark 7. Spray 2 jumbo muffin tins.
In a small bowl combine all of the crumble ingredients, use a fork to mix until the mixture is clumpy and set aside.
¼ cup flour, 3 tablespoons sugar, 2 tablespoons butter, 1½ tablespoons brown sugar, Pinch of salt
In a mixing bowl combine the flour, baking powder, baking soda, and salt. Whisk to combine and set aside.
3¼ cups flour, ½ tablespoon baking powder, ¾ teaspoon salt, ½ teaspoon baking soda
In another mixing bowl add the melted butter, sugar, brown sugar, and eggs. Whisk until combined. Add the buttermilk, sour cream, lemon juice, lemon zest and vanilla and whisk until combined.
1 cup sugar, ¾ cup buttermilk, ½ cup brown sugar packed, ½ cup sour cream, ½ cup butter, 2 eggs, ¼ cup lemon juice, 2 tablespoons lemon zest, 1 tablespoon vanilla
Add the dry ingredients to the liquid ingredients and whisk until smooth, trying not to over mix.
Gently fold the blueberries into the batter. Pour the batter into the muffin tins about 2/3 -3/4 the way full. Top with the crumble.
2 cups blueberries
Bake for 5 minutes at 425°F/220°C then reduce the heat to 375°F/190°C and bake for 20 minutes until the muffins are golden in color or a toothpick inserted comes away clean.
Allow to cool in the pan for 10 minutes before removing and place on a cooling rack to finish cooling.