Hi bmouthboyo
5ltr Stockpots are Ideal for this

Only simmer right at the end Boyo

Slight Update =
2 Kilos Onions.
200ml any vegetable oil
1 medium carrot.
1 Large bulb of Garlic.
3 inch piece of fresh ginger.
A quarter of medium white cabbage.
1 medium green capsicum.
A handful of fresh coriander+stalks.
1tbsp of Salt.
3 litres tap water
Put a lid on and Boil it up for at least an hour.____________________
Add quarter of a tube of tomato puree, or Chefs spoon.
2 tbsp of Mixed Powder. ( for a stronger flavoured base)
keep it on a rolling boil for 20-30mins. switch off, let it cool
or put some gloves on and blend.
Now transfer the sauce to a clean stock pot,
(At this stage I pass the sauce through a food mill/sieve, old school) - optional
Add three cups of boiling water, mix well and bring it back to the boil, covered
with the lid slightly tilted.
keep it on a rolling boil for 20 mins, a froth will start to appear
and eventually form a scum, skim the scum off at the end and discard.
Turn it down to a final 10 minute simmer.You will know when the sauce is ready, when the oil separates and starts rising to the surface.
N.B. Make sure you add enough water to get consistency as in the Video.
Mixed powder in the vid :-
2 tsp Madras Curry Powder
2 tsp Turmeric Powder
1 tsp Coriander Powder
1 tsp Cumin Powder
1 tsp Kashmiri Chilli Powder
0.5 tsp Garam Masala or Kitchen King
Cheers Chewy