This is an amalgamation of my knowledge and what I have learned over the years, it works for me and makes the closest to a curry house madras sauce.
Because you dice the onions finely and cook them until they are golden brown they actually dissolve into a liquid when adding the stock and tomatoes?..you?ll see.  Blending the sauce is optional.  If you do blend just remove whole spices prior to blending with a hand blender. 

Whole Spices
?   4 Green Cardomons
?   1 TS black peppercorns
?   1 TS Cumin Seeds
?   Bit of a Cinnamon Stick

Ground Spices
?   2 TBSP Ground Coriander
?   2 TBSP Ground Cumin
?   1 TBSP Ground Turmeric
?   1 TS Chilli Powder
?   1 TS any spice mix / massala mix (loads on this site)
?   1 TS Salt
?   1 TS Garlic Paste
?   1 TS Ginger Paste

Other Ingredients
?   100ml of vegetable Oil
?   4 Large Onions Finely Diced (this avoids having to blend anything ? you?ll see)
?   1 Tin Chopped Tomatoes - 400g ? BLENDED
?   1 Small Potato sliced into 4 corners
?   1/2 Finely diced Green Pepper
?   400ml Chicken Stock (I just any old chicken stock cube)

Process

1.   Add veg oil to stock pot over high heat
2.   when oil hot add whole spices and heat until they crackle
3.   Add diced onion and reduce heat to medium
4.   Cook onions until they are golden brown (15-20 mins)
5.   Add green pepper and potato cook for further 5 mins
6.   Add Garlic and Ginger Paste ? cook for 2 minutes
7.   Add ground spices & salt, stir and cook for 5 minutes or until spices release their smells/aroma
8.   Add the chopped tined tomato you blended earlier cook for 5 minutes until it starts to darken
9.   Add 400ml Chicken Stock
10.   Reduce heat to low and simmer for 20 minutes
11.   Remove Potato

Use the sauce as your base sauce and make the curry you desire in the usual way.  I don?t bother blending but you can if you like, just remove the oil first and whole spices then blend and return oil.
If you think the sauce is too thick when using to make a curry, say a madras just add a little water, I am convinced this is what the curry house does anyway?..

This sauce works and I swear it?s the addition of the stock, you wait till you add it in towards the end and watch the colour of the sauce with the oil on top.
This base sauce will probably do you 4 curries.

Pics can be found here https://curry-recipes.co.uk/curry/index.php?topic=1581.0


I would welcome feedback as I think this is pretty close as a base sauce.   

Its from my own experience plus a little borrowing from others on the site and even from a book i got a while ago....so really its a bit of everything.

Try it out, but you must dice those onions well or you will need to blend the sauce.

Stew

You can use this one sir, just add 1/2 TS to the base.

Coriander 8 Parts
Turmeric 7 Parts
Cumin 5 Parts
Curry Powder 4 parts
Paprika 4 Parts (optional)

Thats what i love about this old cooking game you can try anything and see what works, its not an exact science...

bart09,

Well done for trying it, it does me everytime i have to say, i swear its the 400ml of chicken stock that elevates it up to a better standard.

Stew

Stew, that sounds good!   I like the fact that I usually have all those ingredients on hand.  BTW, what size tin of chopped tomatoes do you use?  Thanks. 

-Mary