Heat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, leaving enough overhang on two sides to lift out the cooled blondies.

Whisk the melted, slightly cooled butter and packed brown sugar until smooth. Beat in the eggs and vanilla until the mixture looks glossy and evenly combined.

In a separate bowl, whisk the flour, baking powder, salt, cinnamon, nutmeg, and optional apple-pie spice or cloves. Add the dry mixture to the butter mixture and fold just until no dry streaks remain.

Fold in the finely diced, patted-dry apple. Spread approximately half of the batter into the prepared pan, then drizzle or dollop 1/4 cup of caramel sauce over it.

Add the remaining batter and smooth the top carefully. Drizzle with the remaining 1/4 cup caramel sauce and lightly swirl it with a knife.

Bake for 28 to 35 minutes, until the edges are set and lightly browned and the center is just set. A toothpick inserted in the center should come out with moist crumbs, not wet batter.

Cool the blondies completely in the pan for at least 45 to 60 minutes before slicing. For especially clean cuts, chill the cooled pan for 30 minutes, lift the blondies out using the parchment, and drizzle with additional warmed caramel before serving.