Mince the onion and separate the egg yolk from the egg white.

Place minced onion and olive oil in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Let cool.

In a bowl, mix breadcrumbs and milk until combined. Add the cooled onion, remaining meat mixture ingredients, and egg white. Mix until sticky.

Heat salad oil in a frying pan over medium heat. Spread the meat mixture evenly and cook for 5 minutes until browned.

Flip the patty, cover with a lid, and cook on low heat for 7–8 minutes until fully cooked.

Place cheese sauce ingredients in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Stir until smooth.