Cook frozen fries according to package directions until deep golden and crisp.
Season ground beef with salt and pepper, then divide into four loose balls.
Heat oil in a large skillet over medium-high heat until shimmering.
Place beef balls in the pan, cover with parchment, and smash firmly with a spatula.
Cook 2 minutes until edges are crispy, flip, cook 1 more minute, then break into pieces.
Melt butter in a saucepan, whisk in milk and cheddar until smooth cheese sauce forms.
Arrange hot fries in a dish, top with smashed beef pieces, and pour cheese sauce over.
Sprinkle with crispy fried onions and drizzle with burger sauce if using. Serve immediately.
Tip: Press the beef hard for maximum crispy edges.
Tip: Keep the cheese sauce warm so it stays pourable.