According to Dr G G Willis, of the Anglican Patrimony, the December Ember Days (Wednesday, Friday and Saturday this week) replace the old pagan Roman agricultural festival upon which the olives were harvested.
The oldest texts for these days, in the Verona Sacramentary, probably dating from before Christmass fully established its liturgical dominance, still retain agricultural references; but these were gradually eliminated to make way for Advent themes.
Last spring, I bought a tiny but perfectly formed Olive tree in order further to mediterraneanise my garden. It is flourishing (as indeed is my myrtle, which started life as a seedling in the myrtle groves of Parcnasilla in the Kingdom of the West, aka County Kerry).
So, on Wednesday, Pam and I harvested our two olives. It's the sort of thing Traditionalists do.
I expect someone will tell me from personal experience (I don't trust Wikipedia) how I should process them for consumption. Will they fit in with the venison we've ordered for Christmass?