I started cooking eggplant this way because my wife doesn't like it grilled. As it turned out, she doesn't like it this way either. No problem. More for me.
Combine the eggplant, onion, oil, butter, agave syrup, and soy sauce in a stainless steel saucepan with a tight-fitting lid. Season generously with pepper. Cover and cook over medium-low heat, stirring occasionally, for 20–25 minutes, or until eggplant is very soft and sauce is very thick.