Prepare a boiling water bath canner. Heating jars in simmering water until ready to use, but do not boil. Wash lids in warm soapy water and set aside with clean, damage-free bands.
Crush strawberries and measure out the berries.
1-¼ lbs Strawberries
Slice rhubarb into ½ inch pieces.
1 -¼ lbs Rhubarb
In a heavy bottom pot combine the strawberries, sliced rhubarb and stir in pectin.
5 ½ Tbsps. Ball® Classic Pectin
Turn heat to medium and bring mixture to a simmer, cook for 10 minutes without boiling, to help soften rhubarb.
Once the rhubarb has softened enough to press it down with a spoon, heat to high and bring to a full rolling boil that cannot be stirred down, stirring constantly.
Add sugar, vanilla and butter all at once, stirring to dissolve the sugar.
3 ½ Cups Sugar, 1 Teaspoon Vanilla Extract, 1 Teaspoon Butter
Return jam to a full rolling boil. Boil hard 1 minute, stirring constantly.
Remove from heat. Skim foam if necessary.
Ladle hot jam into a hot jar leaving a ¼ 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. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.
Any jars that did not properly sealed should be stored in the refrigerator.