1 Double boiler—(if you don't have one, to DIY you'll need: 1 Large pot and another saucepan that fits into the pot though not directly. What you'll do is fill the bottom of the larger pot with water and put the other pot on top so that the steam from the boiling water cooks the ingredients in the smaller pot without the smaller pot touching the water.)
1 rubber band
1 Grinder (a coffee grinder works best)
1 Large wooden spoon
1 Storage container
1 pound of unsalted butter (about 4 sticks)
1 oz. Finely ground medical marijuana
1. Fill the larger pot with water, not all the way to the top, just some at the bottom.
2. Grind your medical marijuana into as fine a powder as possible.
3. Cut up the sticks of butter into smaller pieces.
4. Put the butter into the smaller pot and place the smaller pot inside the bigger pot. Let it melt
5. Once it is melted, add the medical cannabis and stir it in, removing any clumps or it sticking to the sides.
6. Turn the stove top to a low heat and bring the water to a simmer.
7. Stir the butter and medical cannabis frequently.
8. Lower the heat and add more water. You'll leave the double boiler on the stove for about 4-6 hours, so you'll need to watch the water on occasion to make sure there is enough simmering.
9. PATIENCE is a virtue. Because the steam can only get so hot, you won't burn the butter or the pan. This is why you can leave it on for as long as 6 hours. Leaving it on for that period of time is key as more THC will absorb and bind with the butter.
10. Once the time is up, take the top pot off of the large pot and let it cool for about 5 minutes.
11. In the meanwhile, get your storage container (Tupperware, reused yogurt container, etc.) and secure the cheesecloth over the top of it with a rubber band.
12. Slowly, start pouring the cannabutter mixture through the cheesecloth. Then, with the remaining bud, carefully take the cheesecloth off and squeeze the remaining content into the storage container.
13. Store in the freezer until it hardens, use as needed in any recipe that calls for butter, and place back in the freezer for longer-term storage.
Original Source: Fool-Proof Cannabutter Recipe