Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking pan to prevent sticking.
In a mixing bowl, whisk together the all-purpose flour and granulated sugar to combine evenly.
Pour the melted butter into the dry ingredients and stir until the mixture looks crumbly, with no dry spots remaining.
Add the eggs one at a time, whisking well after each addition, until the batter is smooth and slightly thickened.
Stir in the vanilla extract for a fragrant aroma, blending it evenly into the batter.
Gently fold in the chopped apples, distributing them evenly throughout the batter so each bite will have fruity bursts.
Pour the batter into the prepared baking pan and spread it out evenly with a spatula, smoothing the top for a uniform bake.
Drop spoonfuls of caramel sauce across the top of the batter and gently swirl it in with a knife or toothpick to create a marbled effect.
Bake in the oven until the edges are golden and a toothpick inserted into the center comes out clean, about 35 minutes. The top should look slightly caramelized and bubbling.
Remove from the oven and let cool in the pan for at least 15 minutes to set before slicing into squares.
Serve warm or at room temperature, with additional caramel sauce drizzled on top if desired for extra sweetness.
