Preheat the oven to 350°F (177°C) and line a 9×13-inch metal baking pan with parchment paper, leaving an overhang to lift out the finished brownies (makes cutting easier!). Set aside.

In a small microwave-safe bowl or liquid measuring cup, combine the butter and chopped chocolate. Melt in 30-second increments, stirring after each, until completely melted and smooth. Set aside to slightly cool while you continue.

In a large bowl using a handheld or stand mixer fitted with a whisk attachment, combine the granulated sugar, brown sugar, and eggs. Beat on medium-high speed until the sugar begins to dissolve and the mixture is pale and ribbon-y, about 4 minutes.

Pour the warm melted butter/chocolate into the bowl with the sugar/egg mixture, add the oil and vanilla, and beat or whisk to combine.

Using a fine mesh sieve, sift the flour, cocoa powder, and salt into the batter, then whisk or beat on low speed until combined. Fold in the chocolate chips. The batter will be very thick. Spread evenly into the prepared pan. (A small offset spatula is helpful here.)

Bake for 30 minutes, then test the brownies with a toothpick. Insert the toothpick into the center of the pan. If the toothpick is completely coated in wet batter, return the brownies to the oven for 2 more minutes. If the toothpick comes out with moist crumbs clinging to it, the brownies are done. Err on the side of under-baking, as the brownies will continue to set as they cool. (A completely clean toothpick means the brownies are over-baked!)

Remove from the oven and place on a cooling rack to cool completely in the pan. When cool, lift the brownies out by using the parchment overhangs and transfer to a cutting board. Use a sharp knife to cut into squares.

Cover and store leftover brownies at room temperature for up to 1 week.