If I want to make these brownie more cake like, what ingredients should I add or increase. All that is required off of the box is 1/3 cup water, 1/3 cup vegetable oil and 1 egg.
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I'm no baking expert but here are my thoughts:
Try adding another egg. The white should make the finished product more cake-like. Cut back on the water by an equal amount which should reduce gluten formation making them less chewy. (Crack the egg into the measuring cup then fill it to 1/3 with water.)
And let us know how it works out!
I love the double chocolate. I would not try making the better by adding anything except maybe nuts, or marshmallows or even more chips I would not add more eggs or whatever they are the best. IMHO
I've found that if I replace the vegetable oil with applesauce when baking, the result is usually more cake like.
It's tough to do when you're starting from a mix. From scratch, I would generally recommend switching to butter, and creaming it with the sugar to help make some structure, but since that's not an option for you, the butter might not help.
At the very least, reduce the fat some (by 1-2 T) and add some baking powder for leavening (1/4 t?). Then give your batter a good whisking to aerate it before baking. Using butter instead of oil might still be in your best interest, but I'm not sure how well it would work mixing it in with the flour all at once...
Again, I'm not an expert in this area but I have to disagree, politely of course, with the butter suggestion. Butter, being roughly 20% water, will add to gluten formation, the opposite direction Mrs. T wants to go.