Method

• 1.
  Preheat oven to 200°C. Place sweet potato into an ovenproof dish and roast in the middle of the oven for 45 minutes or until soft all the way through. Split each potato lengthways and scoop out the insides with a spoon.
• 2.
  Place sweet potato flesh, egg, chickpea flour, chilli powder, if using, mustard, nut butter, lemon juice and a pinch of salt flakes in a food processor and pulse until well combined. Transfer to a bowl and stir through the quinoa.
• 3.
  Divide sweet potato mixture into 4 even portions and shape into patties, either by hand or using a food ring the same diameter as your burger buns. Transfer patties to a plate and cover with plastic wrap. Chill for at least an hour (preferably longer), so the patties hold together.
• 4.
  Reduce oven to 180°C.
• 5.
  For the horseradish sour cream, combine horseradish, sour cream and a pinch of salt flakes in a bowl and set aside.
• 6.
  Heat oil in a large non-stick frypan over medium heat. Add patties and cook for 2-3 minutes each side or until they have developed a little colour and a nice surface. Transfer to an ovenproof dish and bake in middle of the oven for 5–10 minutes or until cooked through.
• 7.
  Spread butter on faces of burger buns and grill, butter-side down, for 1-2 minutes or until grill marks appear.
• 8.
  Divide patties among bun bases, dollop on some horseradish sour cream, and top with eschalot and chive. Top with bun lids to serve.