Melt butter in a pan (you need to melt at least twice what you'll use in the recipe because the volume will reduce quite a bit). For a clearer end product, skim the froth off the top as it cooks.
Mix in some marijuana. The amount you use is in your discretion, depending on how strong you want the end-product to be. A general rule of thumb is about 1/8 ounce per stick of butter.
Simmer the marijuana in the butter for a few minutes (10-20 minutes is typical, but it could be more or less depending on the strain and quality of the marijuana), until the butter turns green.
Strain the butter through a fine-meshed strainer. Squeeze hard to wring out as much butter as possible, but be careful not to let any of the grass through.
Use this butter as your recipe directs. If your crust recipe calls for melted butter, use it as-is. Otherwise, chill the green butter until it re-solidifies.