Prepare boiling water canner. Heat jars in simmering water until ready for use. Do not boil. Wash lids in warm soapy water and set bands aside.
Puree strawberries in a blender or food processor until smooth.
Combine strawberry puree with remaining ingredients in a deep pot set over medium heat. Bring mixture to a boil stirring frequently to prevent scorching, lower heat and simmer until mixture is very thick, about 60-90 minutes, stirring frequently. Any foam produced by strawberries will disappear with the cooking process. Strawberry butter is finished cooking when it holds shape on a spoon.
Ladle hot butter into a hot jar leaving a ΒΌ inch headspace. Remove air bubbles. Wipe jar rim. Center lid on jar and apply band, adjust to fingertip tight. Place jar in boiling water canner. Repeat until all jars are filled.
Process jars 10 minutes, adjusting for altitude. Turn off heat, remove lid, let jars stand 5 minutes. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.
