Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Thinly slice the onion. Thinly slice the unpeeled potato, stack the slices, then cut into thin matchsticks. Put the potato on the lined tray, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Bake for 30 mins or until tender.
Step 2 — Cook plant-based patties
Meanwhile, crumble 1 stock cube* into a heatproof jug, add 60ml (¼ cup) boiling water and stir to dissolve. Heat 2 tsp olive oil in a medium frypan over medium-high heat. Cook the plant-based patties for 4-5 mins each side until browned. Remove from the pan and keep warm.
Step 3 — Make onion gravy
Heat 2 tsp olive oil in the same pan over medium heat. Cook the onion, stirring, for 3-4 mins until softened. Stir in the stock and barbecue seasoning (see Kitchen 101) and bring to a simmer. Cook, stirring constantly, for 1-2 mins until thickened. Remove the pan from the heat. Taste, then season with salt and pepper.
Step 4 — Toast buns
Cut the buns in half. Put on an oven tray, cut-side up, and bake for 3-4 mins until lightly toasted. While the buns are toasting, combine 2 tsp olive oil and 1 tsp white wine vinegar in a large bowl and season with salt and pepper. Add the salad leaves and toss to coat.
Step 5 — Serve up
Spread the bun bases with mayonnaise. Top with the patties, onion gravy and salad leaves. Sandwich with the bun tops. Divide the burgers among plates and serve with the fries and any remaining salad leaves. Enjoy!
Step 6 — Kitchen 101
The secret to smooth gravy? Add the stock gradually, stirring constantly, to achieve a creamy consistency. If lumps form, use a whisk and more elbow grease, and whisk until smooth.