Season half of the plain flour with plenty of sea salt and freshly ground black pepper. Dredge the oxtail pieces in the seasoned flour.
Select the Brown/Saute function on the Crock-Pot® Express Multi-Cooker and set the timer for 10 minutes.
After the HEAT display has switched off, add half the butter to the pot and allow it to melt. Add the dredged oxtail pieces, and using the plastic spoon to turn the meat so that it sears on all sides.
Add coarsely chopped vegetables, beef stock, stout, tomato puree and herbs.
Fit and seal the Crock-Pot® Express Multi-Cooker lid, ensuring that the steam release valve is open. Select the Slow Cook option, and set the timer for 8 hours.
At the end of the cooking time, allow the soup to cool. Cover, and place into the fridge overnight.
The next day, skim any fat from the top of the cold soup. Sieve the entire mixture, setting the pieces of cooked oxtail aside, discarding the vegetables and reserving the liquid.
Using two forks (or your fingers) shred the cooked oxtail meat and set aside. Discard the bones and cartilage.
Clean the Crock-Pot® Express Multi-Cooker cooking bowl and place into the heating base. Select MANUAL and press Start.
Add the remaining butter and allow to melt. Add the remaining flour and stir with the plastic spoon for a minute, until cooked.
Slowly add the beef stock, a little at a time, stirring between additions. Bring to a simmer and add the reserved shredded oxtail and the redcurrant jelly.