Why you ask? Because chances are that you are not located near one of the California dispensaries which retails foodstuffs containing cannibas. So you gotta do it yourself. And unless you happen to work in an ice cream shop, you probably won't have access to an ice cream maker, and almost certainly not if you spend all of your disposable income on pot.
You will need:
a generous helping of cannabis sativa, dried and ground (use a coffee grinder)
enough ganja butter for two people to trip out, preferably made with cannabis indica
3/2 tablespoon of vanilla extract
1/2 cup of sugar
1/8 tsp salt
ice (crushed finely) or liquid nitrogen
2 cups of whipping cream
2 coffee cans, 1 lb and 3 lb
cheesecloth (if you can't find this, don't worry the ground up stuff will add a nice texture in the end)
First soak the ground cannabis sativa in the whipping cream for three days. Then strain with a cheesecloth and save that stuff for next time—you can put it in the butter that is going to go in this batch of ice cream. The only note I have to make to herbman's recipe for pot butter is to keep the lid on the pot while cooking, as precious THC will escape in the form of vapor. And don't overcook it! It is possible that the butter will absorb more THC if you fridge it overnight.
Next mix the sugar, whipping cream, salt (not the rock salt), vanilla extract and pot butter in a 1 lb. coffee can and secure the cover with duct tape. Put ice, salt and the 1 lb. can into a 3 lb. coffee can. Secure with more duct tape. Mix for about ten minutes by rolling on floor gently. Let sit for about ten minutes then open it up and
scrape the stuff that has stuck to the insides of the inner can and mix it all back
in. Throw the pecans in now. If the ice or salt needs changing or topping off (some will invariably leak out of the outer can—the trick is to keep it from leaking into the inner can),
do it now. Seal everything back up and mix for five more minutes or so.
Voila! Your ice cream should now be green and soft. Chill overnight in the freezer for it to fully harden.
Enjoy with your favorite topping and beware of owls.
Note: Ice cream is the natural food of stoners and this stuff even moreso. I don't recommend eating after dark, unless you are regularly nocturnal. You want to be awake to enjoy yourself and this stuff will very likely knock you on your ass if done right. And because I am a lazy fuck, I modified Tem42's coffee can method for this node. You can also use a bag if you don't buy coffee in bulk but that seems more messy.