In a pan, heat oil on medium then add the beef; breaking it up as you cook. When it's almost browned, add sugar, distributing it evenly.

Add sliced onion and fry. Add the soy sauce and sake. Cook covered on medium-low heat until the onions are translucent.

Reduce the liquid to your desired thickness, I like mine a little soupy. Leave uncovered until it's cooked to your liking.

Serve in a bowl topped with a soft boiled egg (optional). The picture shows just the yolk arranged on top.

If you'd like, garnish with a couple pieces of diagonally cut leeks.