3 cups flour, divided
3 tablespoons brown sugar
4 tablespoons white sugar, divided
1/2 teaspoon cinnamon
1 teaspoon salt, divided
4 tablespoons butter, frozen
1 teaspoon baking powder
1 teaspoon baking soda
2 eggs, lightly beaten
2-1/2 cups buttermilk
4 tablespoons butter, melted
Zest of 1 lemon
1-1/2 teaspoons vanilla extract
2 cups blueberries
Preheat oven to 350 degrees F and grease a 9-by-13 casserole dish with butter.
Place 1/2 cup of flour in a small bowl and add the brown sugar, 2 tablespoons of the white sugar, cinnamon and 1/4 teaspoon of salt. Mix well to combine.
Grate the frozen butter into the flour and mix together with hands to ensure butter is entirely coated with flour. Place the crumb topping in the in fridge.
In a large bowl, combine the remaining 2-1/2 cups of flour, remaining 2 tablespoons of white sugar, remaining 3/4 teaspoon of salt, baking powder and baking soda.
In a separate bowl combine the eggs, buttermilk, melted butter, lemon zest and vanilla extract. Whisk well. Add wet ingredients to the dry flour mixture, stirring until just fully combined.
Pour the batter into the prepared casserole dish and sprinkle the blueberries on top. Sprinkle the crumb topping over the top of the blueberries and cake mixture.
Place the casserole dish into the preheated oven and bake for 45 minutes, or until the cake is cooked through, the top is golden and the edges have just started to pull away from the sides of the dish.