There are two challenges to deep frying anything -- including French fries -- in bacon grease. Bacon grease has a low smoke point as compared to frying oils, and tends to scorch before your French fries are done. The other problem is that it takes a lot of grease to deep fry anything. To get enough bacon grease for your French fries, you'll have to cook a lot of bacon. For some, this is a problem; for others, it's an excuse to eat more bacon.
Cook bacon and pour the grease into your heat-resistant glass container. Store the container in the refrigerator until you have at least one pint of grease. A quart would be better, but that's more than a year's worth of bacon in many households.
Set up your fire extinguisher near where you'll be cooking. Flash fires are common with deep frying.
Set your cooking pot on the stove over medium heat. Spoon in your bacon grease. Allow to melt like butter.
Insert your cooking thermometer. Heat the grease at medium until it reaches 300 degrees F. Adjust the heat to keep it stable at that temperature.
Sink a handful of fries into the oil. Cover the top of the pot with your splash screen to protect yourself and the kitchen.
Wait until the fries are golden brown -- about 2 to 3 minutes. Remove using your tongs or spider.
Set the finished fries on your paper towel to soak up the extra grease. Sprinkle on the seasonings of your choice.
Add more fries to your oil, cover with a splash screen, fry until gold brown, drain on a paper towel and season. Continue doing this until you've cooked all your fries. You can strain the grease through a coffee filter if it starts to get murky.