Gently break apart the desired amount of weed using a hand-grinder until it’s fine, but not too fine.
Evenly spread weed onto the glass baking dish or sheet pan. Pop in the oven on the center rack for 45 minutes.
Check on the weed frequently while it’s in the oven, gently mixing it every 10 minutes so as to not burn it. You will notice that the color of your herb will change from bright green to a deep brownish green. That’s when you know it has decarboxylated.
In a medium saucepan on lowest heat, add water and butter.
When the butter is melted, add the decarboxylated cannabis. Mix well with a wooden spoon and cover with lid.
Let mixture gently simmer for 4 hours. Stir every half hour to make sure your butter isn’t burning.
After 4 hours, strain with cheesecloth or metal strainer into a container. Let the butter cool to room temperature.
Use immediately or keep in refrigerator or freezer in a well-sealed mason jar for up to six months.