1 cup unsalted butter
1 cup quality medical marijuana trim/bud
2 cups water
2 sauce pans
Bring the water to a boil in a stainless steel sauce pan, then add the unsalted butter. Turn the boil down to a simmer and add the medical marijuana.
Simmer the mixture for three to four hours and add more hot water when needed. Make sure not to let the water get to low and the amount of water isn't extremely important. If you use a large sauce pan just use more water.
Some people boil their cannabutter for less than three hours but we find that we get better results when we boil for at least three hours.
What happens is that the butter being an oil absorbs THC from the resin glands on the medical marijuana. Other cannabinoids also accumulate in the butter. If you have a vaporizer you can even add your "carbolized" or used medical marijuana to the mix. This may help with those who have neurological problems or need strong pain medicine.
After the mix simmers for at least three hours place cheesecloth over a large bowl and pour the mix through the cheesecloth. Have somebody hold the cheesecloth tight or use a large rubber band to hold it on the bowl. This will separate the trim from the butter. It's good to run some pure hot water through the cheesecloth to remove any butter that may be caught up in the cloth. You can simmer a pan of water on the side just before you filter off the marijuana from the butter.
Remove the cheese cloth and put the bowl of cannabutter mix in your refrigerator or freezer to cool down faster. (If you use your freezer be careful not to let the water freeze.) The cannabutter will separate from the water and float on the top of the water. When the cannabutter cools down it will harden.
Don't heat medical marijuana beyond 300 degrees when making butters or oils because it degrades the THC which weakens it's strength.
Once the cannabutter hardens it will cover the top of the bowl. Now you simply poke a hole on the side of the cannabutter and slowly drain off the water that's below the cannabutter.
Cannabutter will last about 1 week in the refrigerator. You can freeze it and get a month or more out if it that way. You can also use this same method to make canna oil by using olive oil and other cooking oils.
Use your cannabutter in any recipe that calls for butter. You can also cut it with regular butter if it is too strong etc.
Source: How To Make Cannabutter