The pudding, developed by chef Blumenthal, contains a whole orange inside, which is revealed when the pudding is cut open. The 'Hidden Orange', features in one of Waitrose's Christmas ads.
After Waitrose sold out in all stores, entrepreneurial customers cashed in, with 195 currently for sale on internet auction site eBay.
The puddings, which retail at £13.99 each, have attracted bids of £62 (with £4.95 post and packing), but individual puddings have been posted with starting prices as high as £330 (with £6 posting).
Brand Republic understands that another 600 puddings are now in production and Waitrose staff are braced for a surge of customer activity when the products hit the shelves.
One staff member in West London said: "They sold out immediately, and with just 600 more coming, we will be lucky to get two boxes more."
A Waitrose spokesman confirmed that a: "relatively small quantity" of additional puddings had been made, and "These will go into our branches mid to late next week and we expect them to sell out quickly."
Blumenthal has been part of Waitrose' marketing strategy since March this year when it was announced he and Delia Smith would front a campaign for the supermarket, created by independent agency MCBD.
The pair extended their link with Waitrose for the Christmas campaigns, planned and bought through Manning Gottlieb OMD, which kicked off in November.