Prepare the Sheet Pan: Preheat the oven to 425°F. Line a rimmed sheet pan with parchment paper and lightly grease the parchment with melted butter or nonstick cooking spray.
Prepare the Dry Ingredients: In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, cinnamon, and salt until evenly combined.
Mix the Wet Ingredients: In a separate bowl, whisk together the eggs, milk, melted butter, and vanilla extract until smooth.
Make the Pancake Batter: Pour the wet ingredients into the dry ingredients. Gently stir with a spatula or whisk just until combined. Do not overmix; a few small lumps are fine.
Add the Apples: Fold the diced apples gently into the pancake batter, distributing them evenly without overworking the mixture.
Spread the Batter: Pour the batter onto the prepared sheet pan. Use a spatula to spread it into an even layer, reaching toward the corners of the pan.
Add the Apple Topping: Arrange the thinly sliced apple pieces over the batter. Sprinkle the brown sugar, cinnamon, and optional chopped pecans evenly over the top.
Bake Until Golden: Place the pan in the preheated oven and bake for approximately 18–22 minutes, or until the pancake is puffed, golden around the edges, and cooked through in the center.
Slice and Serve: Remove the pancake from the oven and let it cool for several minutes. Cut into 12 squares and serve warm with maple syrup and an optional dusting of powdered sugar.