Preheat your oven to 350°F (175°C).
Line an 8x8 inch baking pan with parchment paper, leaving some overhang on the sides.
In a medium bowl, whisk together the unsweetened cocoa powder and boiling water until smooth.
In a separate bowl, combine the chopped unsweetened chocolate and melted butter. Stir until the chocolate is completely melted and the mixture is smooth.
To the melted chocolate mixture, add the vegetable oil, eggs, egg yolks, vanilla extract, and granulated sugar. Whisk until well combined and smooth.
Add the cocoa mixture to the wet ingredients and whisk until combined.
Gently fold in the flour and salt using a rubber spatula until just combined.
Fold in the semi-sweet chocolate chunks until evenly distributed throughout the batter.
Pour the brownie batter into the prepared baking pan and spread it into an even layer. Bake for about 25-30 minutes.
Allow the brownies to cool in the pan for about 10-15 minutes, then lift them out onto a wire rack to cool completely before cutting into squares.