The latest instalment of the BBC One comedy drew an impressive 5.85m (25.4%) at 9pm, beating the previous high of 5.63m (22.3%) set by the series opener on November 27.
QI followed at 9.30pm, bringing in 4.53m (20.4%). Earlier, at 8pm, 4.31m (18.9%) tuned in for Countryfile At Christmas.
Over on BBC Two, The Restaurant bowed out to 1.6m (7%) during the 8pm hour, then the audience climbed to 2.13m (9.4%) during the 9pm screening of Rick Stein's Christmas Odyssey.
The Bill logged 4.06m (17.9%) for ITV1 in its usual 9pm slot.
The penultimate episode of Jamie's Family Christmas took 2.32m (10.4%) for Channel 4 at 8pm, then 1.29m (5.5%) watched Come Dine With Me Extra Portions at 8.30pm. Cutting Edge documentary Teens And Tiaras then had 1.22m (5.4%) at 9pm.
Five's coverage of Everton's game against BATE Borisov averaged 1.1m (4.9%) between 7.30pm and 10.15pm.
Overal, BBC One edged primetime with an average share of 23.6% to ITV1's 22.2%. BBC Two was third with 6.8%, followed by Channel 4 with 5.6% (+1: 0.9%) and Five's 4.3%.
Elsewhere, the season seven finale of Curb Your Enthusiasm managed 77k (0.7%) for More4 between 10.40pm and 11.20pm.
BARB ratings data supplied by Attentional