McDonald's' 'Special Sauce'
McDonald's is selling a limited amount of its 'Special Sauce'McDonald's

One of fast food's most relished 'secret' ingredients has been made available to amateur burger chefs as McDonald's puts bottles of its famed Big Mac Special Sauce up for sale.

However, it will cost you. A limited number of 500ml bottles of its trademark Special Sauce are being auctioned off on eBay.

The first of 200 bottles has been placed on Australia's eBay and the bidding began at a massive AU$18,000 (£9,326).

However, fast food fans have been undeterred by the colossal sum and at the time of writing, after 135 bids, the price has reached AU$23,100 (£11,987).

Not so secret sauce

In a 2012 interview, the restaurant chain's executive chef Dan Coudreaut revealed that the Special Sauce is easily made using store-bought ingredients; mayonnaise, sweet pickle relish and yellow mustard, whisked together with vinegar, garlic powder, onion powder and paprika.

"Big Mac sauce is one of the most iconic McDonald's ingredients and people often ask us where they can buy it; so we're excited to be the first country in the world to offer tubs of Big Mac sauce to our customers," said McDonald's Australia's chief marketing officer Mark Lollback.

"I know of people who love adding our special sauce to all types of food – from French fries to McNuggets – so it's going to be interesting to see what Aussies choose to add a spot of Big Mac sauce to over the next month."

If the price tag of almost AU$1,000/ml is slightly off-putting for you, then fear not. McDonald's will be selling 600 more 25ml tubs in store. The catch? They'll only be available in some of Australia's 920 McDonald's outlets.

McDonald's, however, isn't as greedy as some of its customers, who are willing to pay such an extravagant sum for a bottle of sauce. As its eBay page says: "100% of the auction sale price will go to Ronald McDonald House Charities".