Heat oven to 350°F. Line an 8×8-inch square baking pan with parchment.
Stir ½ cup cocoa powder into ¼ cup hot coffee+¼cup water or water until dissolved. Allow to sit for 5 minutes while you continue with next step, which will allow to cocoa flavor to "bloom."
In a mixing bowl, stir together 1½ cup sugar, ½ cup olive oil, 2 eggs, 1 tablespoon vanilla extract, and ½ teaspoon salt, until everything is well-combined. Stir in cocoa/coffee mixture.
Gently fold flour into chocolate mixture. Fold chocolate chips/chunks into batter if using. Scrape brownie batter out of bowl into parchment-lined pan.
Bake brownies for 35-38 minutes, or until a wooden tester inserted into the center comes out with just a few crumbs.
Remove pan from oven and immediately sprinkle flaky sea salt on top. Allow brownies to cool in pan for about 10 minutes. Carefully lift brownies out of pan with parchment paper and onto a cooling rack and allow to cool completely before cutting, at least 30 minutes. Once completely cooled, cut brownies. Obviously, I didn't allow the brownies to cool, in the pan for five minutes or otherwise.