Heat oven to 350°F and arrange rack in the bottom third. Grease an 8-inch square baking pan and line with parchment paper so there is at least an inch overhanging on two sides.
Combine the 1 1/4 cups light brown sugar, 1/2 cup vegetable oil, and 2 ounces bittersweet chocolate chips in a small saucepan over medium-low heat. Stir frequently until melted and smooth. Pour into a medium bowl and let cool slightly.
Using a paring knife, cut the vanilla bean in half vertically, then using the back of the knife, scrape all the seeds out of the bean. Add the vanilla bean seeds to the chocolate mixture as well as the 2 eggs, and stir to combine.
Sift the 1/2 cup cocoa powder, 1/2 cup flour, 1 tablespoon espresso powder and 1/2 teaspoon salt over the chocolate mixture, then stir with a silicone spoon until thick, shiny, and no flour remains. The batter will be very thick.
Spread the batter evenly into the pan and bake until a toothpick inserted into the center comes out slightly moist, about 25-30 minutes. The top will still be shiny.
Let cool 15 minutes then using the paper, lift out of the pan on to a wire rack to cool completely, or serve warm with a scoop of vanilla ice cream.