The trick is to chill the Mars bar in a fridge for a few hours before cooking.
Prepare a batter mix (the kind you deep fry fish in) and get your oil heated to temperature. Here's a batter recipe I've used before:
Basic Fish Batter (Delia Smith Online)
(You can't fault Delia!)
You can use sparkling water to introduce more bubbles into the batter which gives it a nice texture.
Remove the Mars Bar from the fridge and immediately coat in the batter and cook in the oil right away. Cook until the batter is golden and serve with a scoop of ice-cream.
You can also do this with Snickers bars. It's also worth trying with miniature Mars and Snickers bars.
As a Scotsman I must apologise for inflicting this culinary delight on the rest of the world :)
I would not reuse that oil. The frying-oil reuse that occurs in fast food chains is reuse for the same day or over just a few days. They also store it properly and not just sitting exposed in the fryer.
justkt is correct that more saturated fats are less sensitive to breakdown, this is why bacon grease can be kept for a rather long time.
Three factors play a significant role in oil degradation:
Oxidation
Any contact with air causes oxidation in oil. High temperatures, metal alloys, surface exposure, and even UV light act as catalysts to this reaction.
Hydrolysis
When water interacts with oil it causes it to taste tainted or acidic. This is exacerbated by high temperatures, heating/cooling cycles, and oxidation products.
Polymerizaton
When frying oil deteriorates, the resulting products form both volatile (or reactive) and non-volatile compounds. Non-volatile compounds remain within the frying oil, and can produce polymerization at frying oil temperatures above 200°C (390 F) or in isolated hot spots within the frying system. These molecules bond together to form large, different-sized clusters that accumulate on the oil’s surface. Since they don’t dissolve, they cause foaming; trapping air under the oil, and increase the possibility of hydrolysis.
Given all these, the best environment for any oil is an cold, dark, airtight place. Cold temperatures may cause clouding, but this is not a cause for worry.
Source:
http://www.heatandcontrol.com/technical%20articles/Maximizing%20Cooking%20Oil%20Life.pdf
Best Answer
The other answers touch on the fact that its the release of water from the turkey that interacts with the oil, causes the oil to overflow, and then ignite the burner.
Generally, this happens pretty shortly after you put the turkey in (due do any moisture on the outside of the bird).
To do it safely don't bank on the fact that you've removed all the water - do two additional things:
Do it outside. In the event something bad happens, better to lose some grass on the lawn than your house. If you don't have space outside, you can always go to a public park or such. It may seem like a pain but turkey frying should not be done inside.
There's one absolutely surefire way to ensure than you don't catch the burner on fire by accident. Don't have it on!
@ChrisWalker, below in the comments, also provides a method for making sure you don't put too much oil in the pot and thus cause a spill over.