1. Soak potato fries in cold water for 30 minutes, then drain and pat dry.
2. Heat oil in a deep fryer or heavy pot to 350°F (175°C). Fry potatoes in batches until golden and crispy. Set on paper towels to drain excess oil.
3. In a saucepan, melt butter over medium heat, whisk in flour, and cook for 1 minute. Gradually add stock, whisking until smooth. Simmer until thickened, seasoning with salt and pepper.
4. Layer fries on a plate, scatter cheese curds over them, and pour hot gravy generously on top.
5. Garnish with fresh thyme if desired and serve immediately.