- 3 medium onions
- 1 tblsp olive oil
- 100 g butter
- wholegrain mustard
- black onion seeds
- salt and pepper
- Finely chop the onion and place in a saucepan along with the oil, butter, salt and pepper and onion seeds.
- Cook with a lid on, gently simmering until they are completely softened but no colour.
- Add the mustard and mix well.
- Season and then pour into kilner jar and refrigerate.