Slow Cooked Caramelised Onion Soup

My mum loves to do a lamb roast when we come to visit.  It’s always a winner, as she makes the most delicious gravy with caramelised onions, that really makes the lamb moreish.

It was after visiting my parents just recently and my belly was full with onion gravy and lamb that I decided it has been way too long and that I make a back of onion soup.

It’s been a long time since I have made onion soup. We’ve had pumpkin soup and ham hock soup this winter but no onion soup.

This had to change.

Now the key to a decent onion soup is caramelising the onions beforehand. I’m no stranger when it comes to caramelised onions. But this time around I had planned to let the slow cooker do all the work for me.

Slow Cooked Onion Soup

The original recipe can be found here on The Kitchn.


Part 1 – Slow Cooking the onions

  • 1kg Brown Onions, sliced
  • 2-3 cloves of garlic, finely diced
  • 2 Tbls butter
  • 2 Tbls olive oil
  • Salt
  • Pepper

Part 2 – The Soup

  • 2 Tbls Balsamic vinegar
  • 10 cups of stock

Part 3 – To Serve

  • 50ml Cream
  • Parmesan Cheese
  • Pane di Casa Bread


Part 1 – The Onions

  1. Turn your slow cooker on low, and add the olive oil and butter
  2. Peel, then slice the onions into half moon
  3. Add to the slow cooker bowl
  4. Peel and finely dice the garlic
  5. Add to the slow cooker bowl
  6. Season with salt and pepper
  7. Cover and cook overnight or 8-10 hours

Part 2 – The Soup

  1. Add the balsamic vinegar
  2. Add the stock
  3. Cover and allow to slow cook further for another 6-8 hours

This time is flexible.  You can do it for a shorter period of time, or longer.  The longer you cook it for the more intense the flavour becomes.

Part 3 – To Serve

  1. Just before serving, stir in 50ml of cream
  2. Top parmesan cheese
  3. Serve with bread of your choice

You may think this recipe doesn’t make a lot.  However the flavour is quite intense and rich, so you will eat less of it.

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