1. Cook the brown onion, celery, carrots, beetroot and garlic in a large fry pan with high sides and cook until the onion turns translucent and the vegetables soften.
  2. Add the chicken stock, herbs and salt and pepper and simmer on low for about 5 minutes. Then add the olives and lemon juice and stir through.
    Turn the heat off and transfer the mixture to a food processor and blend until smooth. If you want the sauce runnier then add some water or stock.