Mustardy baked onions

Simple oven-roasted red onions with punchy mustard and balsamic coating make a vibrant side that’s really versatile

  • Prep:8 mins
    Cook:45 mins
  • Serves 4
  • Easy

Nutrition per serving

  • kcal 105
  • fat 3g
  • saturates 1g
  • carbs 17g
  • sugars 14g
  • fibre 2g
  • protein 2g
  • salt 0.3g


  • 4 medium red onions
  • 4 small sprigs rosemary
  • knob of butter
  • 1 tbsp balsamic vinegar
  • 2 tbsp grainy mustard
  • 1 tbsp soft brown sugar


  1. Heat oven to 180C/160C fan/gas 4. Slice the root off each onion to create a flat bottom, then carefully peel, leaving the onion whole. Cut a deep cross in the top of each, then poke in a sprig of rosemary, dot with butter and place in a roasting tray. Pour a little of the balsamic vinegar over each one and season. Wrap the tray in foil and bake in the oven for 30 mins. Meanwhile, mix together the mustard and sugar and set aside.

  2. Remove the tray from the oven, take off the foil and spoon a little of the mustard mixture onto each onion. Return to the oven for 15 mins, uncovered, to caramelise.

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