Preheat the oven to 350°F (175°C). Line an 8×8-inch metal baking pan with parchment paper, leaving overhang on two sides for easy removal. Lightly spray the parchment with nonstick spray and set the pan aside.

Add the butter to a medium saucepan and cook over medium heat until melted, foamy, starts making crackling noises, and deeply golden with brown flecks and a nutty aroma, stirring frequently, then immediately pour into a large heatproof mixing bowl. Let it sit for about 5-8 minutes. Then add the oil and the chocolate mixing until even combined. If the chocolate doesn’t completely melt, pop it in the microwave for 10 seconds and mix.

Whisk in the cocoa powder until glossy and fully incorporated. Allow the mixture to cool to about 120°F; it should feel warm to the touch but not hot, with no visible steam. If its too hot and you add it to the sugar mixture your texture will come out not as chewy,

In a large mixing bowl, combine the granulated sugar, brown sugar, eggs, and egg yolk. Beat with a hand mixer or whisk on medium to medium-high speed for 3–4 minutes, until the mixture is pale, thick, and glossy and falls in ribbons when lifted.

Whisk the vanilla extract and salt into the egg mixture. With the mixer on low speed, slowly pour in the warm chocolate mixture and mix just until fully combined and smooth, being careful not to overmix.

Pour the batter into the prepared pan and smooth the top evenly. Bake for 30-35 minutes, until the edges are set and the center is still slightly soft. A toothpick inserted into the center should come out with thick, glossy crumbs rather than clean.

Remove the brownies from the oven and place the pan on a wire rack. Let the brownies cool completely in the pan for at least 1 hour before slicing, as they will continue to set as they cool.