Method

• 1.
  Peel potatoes and cut into 12mm chips. Place in a large bowl of cold water and soak for 2-3 hours. Drain well, then spread into a single layer on a tray lined with a clean tea towel. Stand for 1 hour to dry.
• 2.
  Meanwhile, make the gravy. Melt butter in a large saucepan over medium-high heat, add onion, garlic and thyme and cook for 6-8 minutes until onion is tender and golden. Stir in flour and cook, stirring occasionally for 2-3 minutes until sandy- coloured. Gradually add stock, stirring continuously, until each addition is smooth and incorporated before adding more.
• 3.
  Once all stock is added, bring to a simmer and cook, stirring continuously, for 3-4 minutes until thickened and gravy no longer tastes floury. Stir in vinegar, season generously, then strain and keep warm.
• 4.
  Just before serving, return to a simmer. Half-fill a large wide saucepan with vegetable oil and heat to 150°C. Deep-fry chips, in batches, for 6-8 minutes until pale golden. Remove with a slotted spoon and drain on paper towel. Increase oil temperature to 180°C. Deep-fry chips again, in batches, for 3-4 minutes until golden brown and crisp. Remove with a slotted spoon and drain on paper towel.
• 5.
  Transfer chips to a bowl, season to taste, add cheeses and half the gravy. Toss to combine and serve hot with remaining gravy alongside.