Preheat your oven to 350°F (177°C) and prepare your pan by lining it with parchment paper.

Whisk together the all-purpose flour, baking powder, and salt in a medium bowl until combined.

Combine the melted butter and brown sugar in a separate bowl, whisking until smooth, then add the egg, egg yolk, and vanilla extract, mixing until blended.

Fold the dry ingredients into the wet mixture gently until no flour streaks remain.

Add the chopped chocolate candy bars, folding them into the batter.

Spread the batter into the prepared pan and smooth the top with a spatula.

Bake for 28–35 minutes until set around the edges and lightly golden.

Cool completely before slicing and serving. Optionally, sprinkle with flaky sea salt.