Sharon, who is played by Letitia Dean, is pursuing a vendetta against Ian, who she blames for the death of her son Dennis.
The episode was praised by some viewers on social media.
One viewer tweeted: "Sharon trying to kill Ian via Christmas pudding is perhaps the best thing ever."
Another said the soap "never disappoints" with its Christmas episodes.
"Top episode that!! Phil (Mitchell) and Sharon will get back together!!! Ian's days are numbered," they added.
The episode was "so good", one viewer tweeted, adding: "I wasn't surprised that it was Phil and Sharon behind Ian's attack but their scenes were so good.
"I think EastEnders at Christmas is at its best."
Actors (L-R) Leslie Grantham, Anita Dobson and Letitia Dean pictured on the exterior set of the BBC soap opera 'EastEnders', January 10th 1985. (Photo by Don Smith/Radio Times/Getty Images)
Actress Letitia Dean pictured on the exterior set of the BBC soap opera 'EastEnders', circa 1986. (Photo by Don Smith/Radio Times/Getty Images)
Actresses Susan Tully (left) and Letitia Dean pictured during the filming of a wedding scene on the set of the BBC soap opera 'EastEnders', September 26th 1986. (Photo by Don Smith/Radio Times/Getty Images)
Some of the BBC Television's EastEnders cast line-up at Elstree Studios at Borehamwood, Hertfordshire, (l-r) Letitia Dean, Susan Tully, Shirley Cheriton, Gretchen Franklin, Wendy Richard, Anna Wing, Sandy Ratcliff and Gillian Taylforth. (Photo by PA Images via Getty Images)
Actors Letitia Dean (left) and Leslie Grantham pictured on the exterior set of the BBC soap opera 'EastEnders', circa 1986. (Photo by Don Smith/Radio Times/Getty Images)
Eastenders stars Tom Watt and Letitia Dean, aka Lofty and Sharon, were mobbed by thousands of cheering fans as they arrived at Herrington Burn YMCA Gala on Wearside 7 June 1987. (Photo by NCJ Archive/Mirrorpix/Getty Images)
July 1987 P000672 (Photo by WATFORD/Mirrorpix/Mirrorpix via Getty Images)
Eastenders stars in Australia, (left to right) Letitia Dean (Sharon) Susan Tully (Michelle).If you've any tea and sympathy to spare around 6.30 pm next Monday, save it for the ABC-TV switchboard operators. Because that's the night Sydney's EastEnders fains will discover that life at Albert Square E20 has ended until next year. And if the crowds at recent Australian appearances of actresses Susan Tully (Michelle Fowler in the series) and Letitia Dean (who plays Sharon Watts) are any indication, there's going to be hell to pay!The two actresses, currently on a flying promotional trip around the World, landed in Sydney recently for interviews and to autograph copies of the EastEnders books. June 29, 1988. (Photo by Guy William Wilmott/Fairfax Media via Getty Images).
Actors (L-R) Letitia Dean, Anita Dobson and Leslie Grantham in a scene from the BBC soap opera 'EastEnders', April 5th 1991. (Photo by Don Smith/Radio Times/Getty Images)
Eastenders actresses (left to right) Letitia Dean, Wendy Richard and Laila Morse at a reception for the Heritage Foundation Awards, at the Grosvenor House Hotel, in London at which Miss Richard won a Heritage Foundation Gold Award. (Photo by Fiona Hanson - PA Images/PA Images via Getty Images)
EastEnders actresses, from left to right Letitia Dean, June Brown and Wendy Richard arrive for the fourth annual British Soap awards at BBC Television Centre in London. The ceremony is hosted by Matthew Kelly. (Photo by Yui Mok - PA Images/PA Images via Getty Images)
LONDON - SEPTEMBER 26: The cast of "EastEnders" attend the Inside Soap Awards 2005 at Floridita, Wardour Street on September 26, 2005 in London, England. (L to R) Petra Letang, David Spinx, Kara Tointon, Billy Murray, Mohammed George (front), Lacey Turner (back), Nigel Harman, Louisa Lytton, Letitia Dean, Geraldine Cowper, Joe Swash, Kim Medcalf, James Alexandrou (front), Tracy-Ann Oberman (back) and Joseph Kpobie. (Photo by Dave Hogan/Getty Images)
Actress Letitia Dean and her partner Darren Bennett are put through their paces during the final dress rehearsal for the first ever tour of Strictly Come Dancing Live! at the SECC in Finnieston, Glasgow. (Photo by Michael Boyd - PA Images/PA Images via Getty Images)
LONDON - JULY 04: Letitia Dean and Claire-Marie Hall attend the photocall for High School Musical Live on Stage at The Hammersmith Apollo on July 4, 2008 in London, England. (Photo by Ferdaus Shamim/WireImage)
Letitia Dean as Ms Darbus during a photocall for High School Musical - Live on Stage at the Hammersmith Apollo in west London. (Photo by Zak Hussein - PA Images/PA Images via Getty Images)
LONDON - MARCH 09: Actresses Letitia Dean and June Brown (R) attend the funeral of actress Wendy Richard at St Mary's Church on March 9, 2009 in London, England. (Photo by Danny Martindale/FilmMagic)
Discover More Like This
BACK TO SLIDE
Another said: "It was an amazing episode of EastEnders.
"I can't believe Sharon and Phil are working together to get rid of Ian.
"I can't wait to see what happens."
A Twitter user added: "That episode of EastEnders was amazing, props to the entire cast and team who worked on it! I'm sat here open mouthed, so many twists and turns."