I found this recipe on a blog I used to follow and enjoy quite a long time called Comfrey Cottages. I found the post and you can view the original here.
Peel off the outer-most bark and allow to sit in a warm, dry place for three days to reduce the moisture content. After that divide it into two equal piles. Add one pile of bark into a preheated double boiler, cover with oil, and let it infuse for about two hours. After that strain the oil and add the second pile of bark to the double boiler and add the infused oil back into the pot for another two hours. (You might need to top of the oil a bit the second time around.) After that strain the oil again and dispose of the second batch of bark like the first (Compost if you like!) Take the finished oil and again, in the double boiler, add 1 ounce of beeswax to every 8 ounces of oil. Once melted together pour it into tins or jars and allow it to cool (Do NOT forget to label.) After it's cooled or in emergencies even if it's still a bit warm it can be used.
This method is considerably faster than the usual means of infusing oil, where you simply add the fresh or dried herb material and leave it to "macerate" for up to 6 weeks. This method is alright if you don't need the oil right away, and the herbs do well with it. But if it's a woody or hard herb (I.E. bark or roots) the boiling method will extract a considerably larger amount of constituents that then "long-brewing" method. And with some herbs, like plantain (Plantago major) for instance, the bacteria, and condensation that the "long-brewing" method produces can sometimes be an issue and make the oil go rancid. However, sometimes this can be remedied by using dried herb (Plantain works well like this.) But, in terms of immediate need, fore-thought, and total prep time, the boiling method is a great way to do it.
