Before you scream, listen: mayonnaise is just eggs and oil pretending to be a condiment. It’s already a brownie’s best friend in disguise. Use ¼ cup of mayonnaise for every ¼ cup of oil.
Your brownies will be the richest, most decadent things you’ve ever baked. No one will taste the mayo. They’ll just ask, “What did you do? This is illegal.” You shrug. You are a baking wizard.
Historical fact: mayo-based chocolate cake was a Depression-era hack. People were desperate. Now you’re desperate for brownies. History repeats itself, but with better frosting.