Heat oven to 350°F. Line an 8-inch square baking pan with parchment paper. (No need to grease—the brownies will take care of that for you while they bake.)
Melt the chocolate in a medium-sized heavy saucepan over a low flame, whisking constantly to prevent any from sticking to the bottom and burning. (You can do this over a double boiler if you prefer.) Remove from heat when there are just a few tiny lumps left, then whisk to finish melting. Add the espresso powder and syrup to the saucepan, and whisk.
To the same saucepan, add the olive oil and vanilla. Whisk. Add the eggs, and whisk until the mixture is smooth. Add the sugar, salt, flour, and cocoa powder, and whisk thoroughly enough to combine and ensure there are no lumps hiding in the batter, but then stop. (Over-mixing will lead to tough brownies—not what we're going for!)
Pour the batter into the prepared pan, sprinkle with the remaining heaping tablespoon of sugar all over, and top with a pinch of flaky salt. Bake until the brownies start to pull away from the sides of the pan and the middle looks puffed up and no longer liquid-y, about 30 minutes. (They won't look fully baked, but they'll set more as they rest.)
Allow the brownies to cool completely in the pan, then cut them into 1-inch squares. For the neatest-possible cut—since they’re so gooey—you can pop them into the refrigerator for 15 minutes before slicing.
Ella Quittner is a contributing writer and the Absolute Best Tests columnist at Food52. She covers food, travel, wellness, lifestyle, home, novelty snacks, and internet-famous sandwiches. You can follow her on Instagram @equittner, or Twitter at @ellaquittner. She also develops recipes for Food52, and has a soft spot for all pasta, anything spicy, and salty chocolate things.