As you are cleaning and grinding up your herb, you should have your crock pot warming up, and set the Pyrex cup full of butter in it while it comes up to temperature. I STRONGLY recommend the use of an oven thermometer so you can monitor the temps when it is cooking.

Once the herb is ground up, add it to the butter in the Pyrex that is sitting inside the crock pot. Stir in the herb as you add it to get a consistent mixture. In other words, do not dump it all in at once then stir... do it gradually.