Hamburger Steaks

Hamburger Steaks
2 Tablespoons olive oil
1 ½ lbs. ground beef, 85% lean
4 Tablespoons frozen butter
½ cup yellow onion, very finely minced
2 teaspoons yellow mustard
3 teaspoons Worcestershire
3 cloves garlic, minced
Salt/Pepper
Gravy
2 yellow onions, sliced into ¾ inch strings
3 Tablespoons cold unsalted butter, separated
1 cup ckicken broth
1 cup beef broth
1 teaspoon onion powder
½ teaspoon garlic powder
1 ½ teaspoons Worcestershire sauce
1/4 cup cold water + 3 tablespoons starch