Ingredients

Crumb Topping

• 1 cup all-purpose flour 
• ⅔ cup granulated sugar 
• ¼ teaspoon kosher salt 
• ½ cup cold butter, cubed 

Cake

• ½ cup chopped crystallized ginger
• 1 ½ teaspoons baking powder 
• ½ teaspoon kosher salt 
• ½ teaspoon ground cinnamon 
• ¼ teaspoon baking soda 
• 2 cups plus ½ Tbsp. all-purpose flour, divided, plus more for skillet 
• ¾ cup butter, softened 
• ½ cup granulated sugar 
• ½ cup packed light brown sugar (all I had was dark and it was fine)
• 2 large eggs 
• 1 ½ teaspoons vanilla extract
• ½ cup sour cream
• 1 cup fresh blueberries (from 1 [6-oz.] container)
• Vegetable shortening, for greasing pan

Directions

1. Prepare the Crumb Topping: Stir together flour, sugar, and salt in a medium bowl; cut cold butter into flour mixture with a pastry blender or fork until crumbly. Cover; chill until ready to use. THIS IS VERY IMPORTANT… WILL MAKE IT MORE CRUMBY1
2. Prepare the Cake: Preheat oven to 350°F. Combine crystallized ginger, baking powder, salt, cinnamon, baking soda, and 2 cups of the flour in a food processor; process until ginger is very finely chopped and mixture is well combined, about 2 minutes. Set aside.
3. Beat butter with a stand mixer fitted with a paddle attachment on medium speed until creamy, 1 minute. Gradually add granulated and brown sugars; beat until light and fluffy, 4 to 5 minutes. Add eggs, 1 at a time, beating until just combined after each addition. Beat in vanilla, 10 seconds. With mixer running on low speed, gradually add flour mixture to butter mixture, alternately with sour cream, beginning and ending with flour mixture, beating until just combined after each addition.
4. Toss together blueberries and remaining ½ tablespoon flour in a bowl. Gently fold blueberry mixture into batter. Spoon into a greased (with shortening) and floured 10-inch cast-iron skillet or oven-proof skillet (at least 2 inches deep). Smooth batter into an even layer using an offset spatula. Sprinkle evenly with Crumb Topping.
5. Bake in preheated oven until a wooden pick inserted in center comes out clean, 50 to 55 minutes. Transfer to a wire rack. Cool 30 minutes to serve warm, or cool completely, about 1 hour.