1Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
2Combine applesauce, white sugar, brown sugar, eggs, and vanilla extract together in a bowl. Whisk flour, baking soda, salt, and cinnamon together in a separate bowl. Add flour mixture to the egg mixture, alternating with buttermilk just until batter is moistened. Fold coconut and walnuts into batter; pour into the prepared baking dish.
3Bake in the preheated oven until a toothpick inserted near the center comes out clean, 45 to 55 minutes. Cool on a wire rack. Dust coffeecake with confectioners' sugar.
1 cup applesauce (such as Mott's® Natural Applesauce)
1 cup white sugar
1 cup packed brown sugar
1 teaspoon vanilla extract
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 teaspoon ground cinnamon
1 cup buttermilk
1 cup flaked coconut
1 cup chopped walnuts
1 tablespoon confectioners' sugar, or to taste (optional)