Preheat the oven to 350°F. Spray a 9x13-inch baking pan with flour-based non-stick spray.
In a medium bowl, combine 2 tablespoons butter, walnuts, 1/3 cup granulated sugar, brown sugar, cinnamon, and salt. The mixture will be crumbly. Set aside.
Whisk the flour baking soda and salt in a separate medium bowl and set aside.
In a large bowl, use a mixer to cream together the remaining 1 cup granulated sugar and 1/2 cup butter. Add the sour cream, apple cider vinegar, and vanilla extract, mixing to incorporate. Add the flour mixture and continue mixing just until combined; do not overmix. Gently stir in the apples. The batter will be thick.
Transfer the batter to the prepared baking pan, using a spatula to spread it evenly. Sprinkle the streusel mixture over the top to cover completely.
Bake 45 minutes, or until a toothpick inserted in the middle of the cake, comes out clean. Let the cake cool to room temperature then serve.