A traditional brownie box mix calls for water, eggs and vegetable oil. Doctored up brownie ingredients. Stir powdered sugar into the peanut butter. How to make brownie mix taste homemade. When you use melted butter, allow it to cool before adding it to your batter so it does not begin to cook the eggs. But we have a few ingredient swaps that will make box brownies taste like bakery brownies! 1 Box brownie mix All ingredients listed on box, BUT make these changes: add 1 extra egg; use melted butter in place of oil; add extra 2 TBS butter; use milk in place of water; add extra 4 TBS milk; Note: Adding the extra egg will make the brownies more cake-like. It’s all about adding ingredients to the brownie mix to give the brownies better texture & taste. Plop(yes technical cooking term) the peanut butter over the top of the brownie mixture … This will create more air pockets and result in brownies with a cake-like crumb. Heat the peanut butter in the microwave for 15-20 seconds or until slightly runny. If you only soften the butter, you will need to cream it with the sugar to mix it properly. Mix the brownies per the package directions. If you prefer a more dense/chewy brownie, then leave out that extra egg.