I first had this sauce in a restaurant in Austin, Texas with a breaded chicken escalope when I was about 10 years old and the memory of the sauce has stuck with me ever since. That's how darned good it is and I've spent years trying to nail it down
The main aspect of the sauce you want to focus on is the cooking liqueur as this is the basis of flavour and the peas give it thickness. If you want to 'heat' the sauce up a bit then why not add a sprinkling of cayenne pepper at the end?
Start off by making the cooking liqueur as this is the basis that gives the sauce its main flavour. Crush the black peppercorns and chilli flakes in a pestle and mortar and add into a sauce pan on a low heat to warm them through. You'll hear a popping noise and this is when you add the oil and bring up to a medium heat
Add in the carrot and celery and begin to sweat down, stirring frequently to avoid burning. After a few minutes add the onions and continue to sweat down for a few more minutes before adding the garlic and mustard. Cook for a further minute
Now add the white wine and reduce this by a 1/3rd as we want to burn off the alcohol and leave the flavour. Add the stock and bring to the boil before taking off the heat, placing a lid on the saucepan and leaving to infuse while it cools.
Once cool, strain the cooking liqueur through a sieve and introduce the cooking liqueur to a clean sauce pan and bring to the boil
Strain the black eyed peas and give a rinse before adding into the boiling cooking liqueur, turning down the heat to a simmer and placing a lid on top and leave to simmer for 20 minutes.
Strain again through a sieve and reserve the bean cooking liqueur.
I usually like to take the flavoured beans and blitz them in a food processor with some cooking liqueur and then pass the blitzed beans through a fine sieve into a clean sauce pan to make it really smooth
Add cream to the pureed beans and stir over a low heat until incorporated. Add the butter and melt. If the sauce is too thick, add some reserved stock to loosen and remove from the heat
At this point you can cool and keep in the fridge until needed or serve hot straight away