Pre-heat the oven to 350 degrees F. Cover an 8×8 inch square baking pan with two pieces of foil so that it comes up both sides of the pan. Grease the foil with butter or coat lightly with cooking spray. Melt the butter in a large bowl and let it cool. Then add the oil and both the brown and white sugar, to the melted butter. Whisk well to combine. Add the Beer Malt Vinegar and continue to whisk until the batter turns creamy and lighter in color. Add in the vanilla, salt and then add the eggs one at a time and continue whisking. Add the flour and gently fold into the batter with a spatula or wooden spoon, until just combined. Do not over mix the batter. Then gently fold in the cocoa powder. Mix in ½ cup of chocolate chips or chunks.