This is so simple but one of the most pleasing things coming out of our kitchen at HK, we like to keep things as simple as possible and not impart any unnecessary flavours so use water as our base. We have also made this with meat and vegetable stocks as the base which adds another dimension.
15 brown onions
No that’s really it
(Roscoff’s makes the best broth but availability isn’t likely in supermarkets. Italian white onions are also good, but seriously this is delicious with a big standard brown or Spanish onion)
Peel and then half your onions, leaving the root on so they stay in halves, this is important.
Sear off the flat side of every onion in a deep stock/sauce pot with the rapeseed oil, you will not have enough room to do them all at once so work in batches and put to one side on kitchen towel to drain while finishing the other onions. You are looking for an extremely caramelised brown onion.
Once all onions are seared, wipe any excess oil from the pan, but leave the caramelisation from the onions in the pan.
Place the onions back into the pan and top up with water so all the onions are covered.
Bring to a simmer, and let simmer but not boiled for 40 minutes, then remove from the heat and let sit with a lid for 2 hours.
Top back up with water and bring back to a simmer for 20 minutes then again let sit with a lid for 2 hours.
Remove lid and skim any oil (if any) from the top of the liquid
Next remove all onions from the pan and discard, this may seem wasteful, and you can use the onions for a purée if wanted however they have lost all flavour to the stock and no longer have any value.
Pass the stock through a fine strainer and simply bring to the boil and reduce.
How far you reduce is up to you – keep it light and add to a gravy, reduce to a syrup and finish with pepper and cream for a steak sauce, or in between as we do in the restaurant.
We finish the broth with a minus 8 vinegar to add some balance and acidity.