Heat oven to 350°F. Line an 8×8-inch square baking pan with parchment paper, extending it up the sides. Coat any sides or corners of the pan left exposed with nonstick spray.

Place chocolate and olive oil in a large bowl and melt it most of the way over gently simmering water or in a microwave in 30-second bursts. Off the heat, stir until smooth and fully melted. Whisk in sugar, cocoa, and salt until combined, then whisk in eggs, one at a time, followed by vanilla. Stir in flour and scrape batter into prepared pan, spread until even, then sprinkle lightly with flaky salt. Bake for 30 minutes to 34 minutes, or until a toothpick inserted into the center comes out batter-free.

Transfer to a rack and let cool for 10 minutes. Then, use the parchment paper to gently yank the brownies out of the pan onto the rack. Let cool another 10 minutes if you can bear it, then cut into 16 squares. Nobody knows why, but trust me that a disposable plastic knife is the easiest way to cut brownies cleanly, even when hot.

Do ahead: I like to keep leftover brownies in the fridge for peak fudginess. Brownies will also freeze well tightly packed in an airtight container, for at least a month.