McDonald's secret Big Mac special sauce has been a mystery for years, but for the first time you can buy a bottle of it - too bad it's running for $18,000 Australian dollars on eBay. We have a recipe for you to try at home, so you can recreate and find out just what's in McDonald's secret Big Mac special sauce!

According to CNBC.com, only 200 of the 500ml limited edition bottles are being sold worldwide, with proceeds going to charity. On Tuesday morning, "Bottle #1" had a bid price on eBay of 23,100 Australian dollars ($17,702), with eight days left of the auction.

For now the sauce is only available in Australia but McDonald's might roll out the McDonald's secret Big Mac special sauce worldwide - but no word on when the next limited edition bottle will go on sale yet.

Proceeds from the eBay auction will go to the Ronald McDonald House Charities, which helps seriously ill children and their families.

In case you don't have $18,000 Australian dollars to spare, here's a recipe that'll help you find out just what's in McDonald's secret Big Mac special sauce!

According to TopSecretRecipes.com, McDonald's secret Big Mac special sauce ingredients are a combination of mayonnaise, French dressing, sweet pickle relish, white onion, white vinegar, sugar, and salt. All you have to do is combine these ingredients, chill it for several hours or overnight, and then slather away!

So far, this recipe has gotten some great reviews, with maybe people saying that this combination of ingredients tastes "nearly identical" to McDonald's true Big Mac version.

Click here to test it out for yourself!