This is a simple process during which you heat up the butter several times to remove the excess moisture in it. I always put the Crock-Pot on low only, mostly because I have a tendency to forget about the pot and I know if I leave it on low it won’t burn.
Step 1:
Heat the butter until the side of the Crock-Pot feels uncomfortable to the touch of your full palm, then turn the Crock-Pot off. Skim off the foam that has risen to the top of the pot.
Step 2:
Repeat this twice more, each time letting the butter cool fully before you reheat it. After skimming the third time, add the marijuana leaf.
Step 3:
Stir. Bring to a simmer. Continue to simmer, stirring occasionally, for 1-2 hours.
Step 4: Cool for up to 8 hours. Then, in a new series of heatings and coolings, repeat heating, stirring and cooling down 2 more times. The increase in potency it produces is worth the investment in time. By the third heating, the butter will have a thicker consistency.
Step 5:
Set a strainer with a relatively fine mesh on top of a large measuring bowl. The bowl will catch the strained butter.
Step 6:
Slowly pour the butter into the strainer. Use a large serving spoon to press the remaining butter out of the leaf material. Squeeze out as much of the remaining butter as you can.
Step 7:
Pour the butter into a measuring cup.
Step 8:
Put the finished product in 1-cup containers, ready to use when needed. 
Method II: Ground Marijuana in Oil
This method is less time consuming and lower in fat than the butter method, but something is lost with regard to flavor when using the oil infusion as opposed to the butter infusion.
Step 1:
Place 6 cups of canola oil in a Crock-Pot.
Step 2:
You do not have to clarify it. Set the Crock-Pot on low and allow it to heat up until the Crock-Pot is too hot to press your hand against. Prepare the marijuana leaf as described in method I, (4 ounces), then pour it into the Crock-Pot and stir.
Step 3:
Let sit for 3 days, reheating the mixture each day, and straining as in method I on the third day, as follows.
Step 4:
Pour through a strainer into a large measuring bowl.
Step 5:
Press the remaining oil out of the leaf material.
Step 6: Discard the leaf material. Here is how the finished oil looks:
You can keep the finished oil in a canning jar or any other suitable tightly sealed container in the refrigerator for up to 8 weeks.
Method III: Whole Marijuana in Water with Butter
The following uses water with the marijuana and butter. Simmering the cannabis in water helps to break down the active ingredients. Because THC+ is only soluble in fat or alcohol, these active ingredients end up in the butter and the water can be discarded with no reduction in potency. This method also retains the cream in the butter as the butter is not clarified. This helps to produce a richer cookie, such as a shortbread, if that is important to the patient. It also eliminates the need to grind the marijuana. It does, however, require a larger pot and the need to refrigerate for an additional 24 hours. If time is a consideration, you may want to stick with method I.
Step 1:
Fill a large pot about half full with water. Add marijuana. This process does not require the careful cleaning or grinding needed in methods I and II. You can even use stems and whole leaves. I use 1 ounce of marijuana for one pound of butter. If the final product turns out to be too potent for you, reduce the amount of herb. Increase if a more potent medicine is needed.
Step 2:
Bring to a boil, stirring once or twice. Reduce to a simmer and continue simmering for about 1 hour.
Step 3:
Add butter in proportion to amount of marijuana used. The butter does not need to be clarified. Slowly return to a simmer, stirring gently. Simmer for at least 1 hour. Remove from heat and allow to cool completely. Repeat the simmering/cooling process twice for the most potent butter. I usually do this over 2 days, covering the pot while it cools.
Step 4:
Now come the preparations for straining. Do this step right after the final simmering while the water is still hot. Use caution as the pot can be heavy. Find a second pot or bowl, at least as large as the first. Place a strainer or colander over the pot. Place a piece of cheesecloth over the strainer or colander. The cheesecloth can be eliminated, but I find it makes it easier to separate the herb from the water.
Step 5:
Slowly pour the butter/water/herb mixture over the strainer. Allow to cool.
Step 6:
When it is cool enough to handle, fold the cheesecloth around the herb and lift it out of the strainer.
Step 7:
Twist the cheesecloth bundle and press with the back of a spoon. To recover the maximum amount of butter, pour 1-2 cups of boiling water over the herb while it rests in the strainer. Allow to cool enough to squeeze out this additional water. Discard the herb.
Step 8:
Now we’re ready to refrigerate. Pour liquid into a pot that will fit in your refrigerator. Cover, let cool, and then refrigerate this water/butter mixture for at least 24 hours. The butter will harden on top of the water.
Step 9:
After the mixture has been refrigerated for 24 hours, it’s time to separate the butter from the water. Cut a pie-shaped piece of butter and remove it from the water.
Step 10:
Pull off remaining chunks of butter.
Step 11:
To dry the butter, place the chunks of butter on a towel (paper towels will work) and gently pat excess water off of the bottom of the chunks.
Step 12:
The surface of the butter that has been in contact with the water may be mushy. Gently scrape if desired. I save this mush to use in a recipe like the one for brownies, which will tolerate the addition of some water.
Step 13:
You will now have several chunks of beautiful light green butter. Place them in a small pan and melt until you again have a liquid.