Things You’ll Need: Liquid dish soap (Dawn works best), Stain remover, like Grandma’s Secret Spot Remover
Baking soda, Liquid laundry detergent, like Tide

Dish Soap Method

Squirt a few drops of liquid dish soap on the butter stain, then let it sit for a few minutes.  You can use an old toothbrush to work the soap into the stain.  Rinse well.  Then use a dab of stain remover and wash the fabric in hot water.  Just be sure that the stain is completely gone before you put it in the dryer.  If not, the butter stain may set permanently!

Baking Soda Method

For delicate clothing, try baking soda.  Baking soda absorbs the grease stain without needing to scrub.  Cover the stain with a generous sprinkle of baking soda, then let it sit overnight.  Shake off the baking soda and wash the clothing in hot water.  This also works great on carpet and upholstery because you can simply vacuum up the baking soda after letting it absorb the stain overnight.  Repeat as needed.