How to preserve fresh herbs in Oil or Butter.
From Organic Gardening, Vol. 59:6, page 24

  • Wash herbs, discarding stems and damaged leaves.  Spin leaves dry in a salad spinner or dry well with paper towels.
  • Place herbs in a food processor with 1/3 cup olive oil for every 2 cups leaves, or 1/2 cup (1 stick) unsalted butter per 2 to 4 tablespoons leaves.
  • For butters, add grated citrus rind, ginger or garlic for extra flavor.
  • To make sure herb oils are adaptable to a wide range of uses, don’t add cheese or nuts.
  • Pulse processor, scraping down sides of bowl from time to time, until you get a chunky paste and all leaves are chopped.
  • To package for freezing, put 1 cup herb oil or 1/2 cup herb butter in a 1-quart zip-top bag, then flatten and spread mixture to make a thin layer.  Freeze flat.
  • Best when used within 6 months.

Use herbs preserved in oil the same way that you use fresh herbs.  Use herb butter the same way that you use butter.