Preheat your oven to 350°F (175°C). This ensures that your brownies will bake evenly and come out perfectly fudgy.
Line a 9x9-inch baking pan with parchment paper, leaving some overhang on the sides. This will make it easier to lift the brownies out once they are baked.
In a large mixing bowl, combine the semi-sweet chocolate chips and unsalted butter. Microwave in 30-second intervals, stirring in between, until completely melted and smooth.
In a separate bowl, whisk together the cocoa powder, cornstarch, salt, and granulated sugar. This step ensures that all dry ingredients are well combined and ready to mix.
To the melted chocolate mixture, add the room temperature eggs and vanilla extract. Whisk until fully combined.
Gradually add the dry ingredient mixture to the chocolate mixture, stirring until just combined. Be careful not to overmix; you want the brownies to remain fudgy.
Using a spatula, gently fold in the Heath toffee bits, ensuring they are evenly distributed throughout the brownie batter.
Pour the brownie batter into the prepared baking pan, spreading it evenly. Bake in your preheated oven for about 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan on a wire rack. Once cooled, use the parchment overhang to lift the brownies out of the pan. Cut into squares and enjoy!