Preheat oven to 350° F. Line a rectangular baking pan (9x13 inches) with parchment paper and lightly spray with baking spray. Set aside.
Place butter and sugar in a large microwave-safe bowl. Microwave for 30 seconds, then remove and stir with a whisk. Repeat process 2-3 more times until the mixture looks glossy and the butter is completely melted. Allow mixture to cool slightly.
Add oil, yogurt, and vanilla extract; mix until well incorporated. Add in cocoa powder and continue mixing until incorporated.
Add 1 cup flour mixture and baking soda; mix until combined. Add buttermilk and vinegar; mix until combined. Add remaining flour and mix until just combined. Please DO NOT overmix the batter.
Pour the mixture into the prepared pan and bake. For fudgy brownies, bake for 30-35 minutes. For cakey brownies, bake for 35 -40 minutes, or until set and a toothpick inserted in the center comes out with just a few moist crumbs.
Let cool completely before cutting. Use a large serrated knife to cut brownies in the desired size.
FOR SUPER FUDGY BROWNIES, add 1 cup (200 g) of chocolate chips or chunks to the batter (step 4).STORE: The brownies will stay fresh in an airtight container at room temperature for up to 4 days.FREEZE: Unfrosted brownies freeze well, up to 2 months. To freeze brownies, make sure that they are suitably wrapped to reduce the risk of freezer burn. Wrap them individually in plastic wrap and then with foil.To thaw the brownies, unwrap them from the foil and plastic wrap and let them stand at room temperature for 3-4 hours before eating.LOOKING FOR MORE EGGLESS RECIPES?