Preheat oven to 350°F. Grease and flour a 9x13-inch baking pan and set aside.

To make the topping, combine flour, both sugars, salt and cinnamon in a medium bowl. Add melted butter and stir until the mixture resembles coarse crumbs; set aside.

In a medium bowl, whisk together flour, baking powder and salt. Set aside.

In a large bowl, beat butter and both sugars on high until light and fluffy, about 5 minutes. Add eggs one at a time, mixing well after each addition. Stir in the vanilla extract, lemon zest and lemon juice.

Combine buttermilk and sour cream in a small bowl.

Alternate adding dry ingredients and buttermilk mixture to the butter sugar mixture, starting and ending with the dry ingredients, mixing just until combined after each addition. Fold in blackberries and pour into prepared pan, spreading out into an even layer. Sprinkle with topping and bake until a toothpick inserted in the middle comes out clean, about 50 minutes to 1 hour. Remove from oven and let cool completely before slicing and serving. Enjoy!