Preheat your oven to 350°F (175°C). This ensures that your blondies bake evenly.
In a microwave-safe bowl, melt the butter. Let it cool slightly before mixing it with the sugar.
In a mixing bowl, combine the melted butter and dark brown sugar. Whisk until smooth. Then, add the egg and vanilla, mixing until fully incorporated.
In a separate bowl, whisk together the flour, salt, and baking soda. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Gently fold in the Heath bar chunks and semi-sweet chocolate chunks until evenly distributed throughout the batter.
Pour the batter into a greased or parchment-lined 8x8 inch baking pan. Spread it evenly and bake for 20-25 minutes, or until the edges are golden and a toothpick inserted in the center comes out with a few moist crumbs.
Allow the blondies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely. Once cooled, cut into squares and serve.
