Preheat your oven to 350°F (175°C). While the oven heats up, line an 8×8-inch baking pan with parchment paper.
In a large mixing bowl, sift together the flour and cocoa powder.
In a separate bowl or a large measuring cup, combine the water, vegetable oil, vanilla extract, and apple cider vinegar. Whisk until they are well mixed.
Pour the wet ingredients into the bowl with the dry ingredients. Using a spatula or a wooden spoon, gently fold the mixture together until just combined.
Pour the brownie batter into the prepared baking pan, spreading it out evenly. Smooth the top with your spatula to ensure the brownies bake uniformly.
Place the pan in the preheated oven and bake for 20–25 minutes.
* To check if they’re done, insert a toothpick into the center of the brownies. If it comes out with a few moist crumbs, they’re ready. If it comes out with wet batter, give them a few more minutes.