Heat the oven to 350°F (175°C) and grease a 9 x 13-inch baking pan. Set the prepared pan aside so the thick batter can be added immediately after mixing.

In a large bowl, whisk the eggs, granulated sugar, neutral vegetable oil, and vanilla extract until the mixture looks smooth and evenly blended. A hand whisk is all you need for this one-bowl batter.

In a separate bowl, stir together the all-purpose flour, baking soda, ground cinnamon, and salt. Distributing the leavening and spices through the flour helps them spread evenly throughout the cake.

Add the dry ingredients to the egg mixture and stir just until no large streaks of flour remain. The batter will be fairly thick, so avoid mixing longer than necessary.

Fold in the finely chopped apples and chopped walnuts until they are distributed throughout the batter. Use a spatula and gentle strokes to protect the tender texture.

Spread the batter evenly into the greased 9 x 13-inch pan. Smooth the top so the cake bakes at a consistent thickness from edge to center.

Bake for 50–60 minutes, checking the thickest center portion near the end of the baking time. The cake is ready when the center is set and a toothpick comes out clean or with a few moist crumbs.

Cool the cake in the pan before slicing into squares. Serve it plain, with whipped cream, or with a light powdered-sugar glaze once it has cooled enough to cut neatly.