Best Moist Apple Cake

Ingredients

• Cake:
• 2 cups all-purpose flour
• 1/2 cup whole wheat flour
• 1 teaspoon baking soda
• 1 teaspoon baking powder
• 1 teaspoon salt
• 1 teaspoon cinnamon
• 1 1/4 cups vegetable oil
• 1 1/2 cups white sugar
• 1/2 cup brown sugar
• 3 eggs
• 1 teaspoon vanilla
• 4 apples, thinly sliced
• 1 1/2 cups finely chopped walnuts
• Topping:
• 1 cup brown sugar
• 1/2 cup butter
• 1/4 cup milk
• 1/2 cup finely chopped walnuts