Adjust oven rack to middle position and preheat oven to 350°F.
Grease cake pan with butter.
For Crumb: Combine melted butter, brown sugar, and sugar in a bowl.
Stir in cinnamon, ginger, salt, and flour until mixture is the texture of wet sand. Let chill in the refrigerator while making cake.
For Cake: In a medium bowl whisk together flour, baking powder, baking soda, and salt; set aside.
In the bowl of a food processor fitted with a paddle attachment, cream together butter and sugar. Add eggs and vanilla extract and beat to combine.
Beat in ½ dry ingredients, followed by the sour cream, and then the remaining dry ingredients.
Use a rubber spatula to gently fold in berries.
Pour cake batter into prepared pan and smooth top. Break crumb into ½-inch pieces and sprinkle evenly over top of cake. Bake until crumbs are golden and a cake tester inserted into the middle of the cake comes out clean, about 50 minutes. Let cool 10 minutes before releasing from pan.
Recipe by Amish 365 at https://www.amish365.com/blackberry-crumb-cake/