Prepare the Oven and Pan: Preheat the oven to 350°F (175°C). Grease a 9 x 13-inch (23 x 33 cm) metal baking pan. Line the bottom and two long sides with parchment paper, leaving a slight overhang for easier removal. This will help prevent the cake from sticking and make it easier to lift out once baked.

Prepare the Apples: Peel and core the apples, then cut them into pieces approximately 1/2 inch (1.25 cm) wide. Measure 3 cups (360 g) after cutting. Keeping the pieces fairly uniform ensures they soften at the same rate during baking, which is crucial for the cake's texture.

Combine the Dry Ingredients: In a medium bowl, whisk together the flour, cinnamon, baking soda, baking powder, and salt. Break up any compacted flour and ensure the leavening agents are distributed evenly. This step is important for achieving a light and fluffy cake.

Mix the Wet Ingredients: In a large bowl, whisk the eggs, oil, brown sugar, granulated sugar, and vanilla for about 1 minute. The mixture should look smooth, glossy, and evenly blended, without visible streaks of egg. This ensures that the sugars dissolve properly and the cake has a uniform sweetness.

Make the Batter: Add the dry ingredients to the wet mixture. Fold with a flexible spatula until only a few small flour streaks remain. The batter will be thick and may require firm folding rather than whisking. This technique helps maintain the cake&x27;s structure while incorporating the ingredients.

Add the Apples and Nuts: Fold in the diced apples and optional toasted walnuts or pecans. Continue folding until the fruit is evenly distributed and no dry flour remains. The batter should look heavily filled with apples but still hold together around them, which is essential for the cake's final texture.

Fill the Pan: Transfer the batter to the prepared pan. Spread it evenly into the corners and smooth the surface. Press any exposed apple pieces lightly into the batter so they do not dry out during baking. This helps ensure that the apples bake evenly and stay moist.

Bake the Cake: Bake on the center rack for 42 to 48 minutes. The top should be deep golden, the center should spring back lightly when pressed, and the edges should begin pulling slightly away from the pan. This indicates that the cake is nearing doneness.

Check for Doneness: Insert a toothpick into the center in an area without a large apple piece. It should come out clean or with a few moist crumbs. Wet batter indicates that the cake needs another 3 to 5 minutes. This step is crucial to ensure the cake is fully baked.

Protect the Surface if Needed: If the top becomes dark before the center is baked, place a loose sheet of aluminum foil over the pan and continue baking. Do not seal the foil tightly around the edges, as this can trap steam and affect the cake's texture.

Cool in the Pan: Place the pan on a wire rack and let the cake cool for 30 minutes. The crumb will be delicate while hot because of the amount of fruit, so it's important to let it set before attempting to remove it.

Finish Cooling: Use the parchment overhang to lift the cake from the pan, or leave it in the pan for serving. Cool for another 30 minutes, until the center is no longer warm. This allows the flavors to meld and the texture to firm up.

Finish and Slice: Dust the cooled cake with powdered sugar, if using. Cut it into 15 pieces with a sharp knife, wiping the blade between cuts if moist crumbs collect on it. This helps achieve clean slices for a better presentation.