Cauliflower Cheese Pithivier

5 Mins | 1hr 5 min

  • ½ tbsp olive oil
  • 2 red onions, sliced
  • 2 tsp balsamic vinegar
  • 1 tsp dark brown sugar
  • 1 tsp fresh thyme leaves
  • 600g cauliflower, broken into florets
  • 40g unsalted butter
  • 1 tbsp flour, plus extra for dusting
  • 300ml milk
  • 100g strong Cheddar, grated
  • 375g (about 3) leeks, trimmed and sliced
  • 2 x 375g packs ready-rolled light puff pastry
  • 1 egg, beaten