Make the crumb topping. Preheat the oven to 350°. In a medium sized mixing bowl combine 1 ¼ cup all purpose flour, ½ cup granulated sugar and ½ cup brown sugar. Add in ½ cup melted salted butter and mix until crumbly. Set aside.
Dry ingredients. Spray a 9x13” baking dish with cooking spray and set aside. In a medium sized mixing bowl combine 2 cups cake flour, 1 ⅓ cup all purpose flour, 1 ½ teaspoon baking powder, 1 teaspoon salt and ½ teaspoon baking soda. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment combine 1 ½ cup sugar and ¾ cup salted butter, at room temp. Beat together on medium speed for about 2 minutes, until smooth.
Add in ½ cup vegetable oil and mix to combine. Add in 4 large eggs and mix for 30 seconds.
Add in ⅔ cup buttermilk, ⅓ cup sour cream and 2 teaspoons vanilla extract and mix to combine. Add in the flour mixture and mix until just combined.
Prep strawberries. In a large mixing bowl combine 3 cups chopped strawberries, ¼ cup sugar, 3 Tablespoons cornstarch and 1 Tablespoon lemon juice.
Assemble the cake. Transfer the cake batter into the prepared baking dish and smooth out. Spoon strawberries on top in an even layer, then use your hands to crumble the topping on top.
Place in a preheated oven on the center rack and bake for 45-50 minutes., or until a toothpick inserted into the center comes out clean or with a few moist crumbs.