prepared fruit (buy about 1 qt. fully ripe strawberries and 1 lb. fully ripe rhubarb)
sugar, measured into separate bowl
butter or margarine
Bring boiling-water canner, half full with water, to simmer. Wash jars and screw bands in hot soapy water; rinse with warm water. Pour boiling water over flat lids in saucepan off the heat. Let stand in hot water until ready to use. Drain jars well before filling.
Stem and crush strawberries thoroughly, one layer at a time. Measure 2-1/4 cups prepared strawberries into 6- or 8-qt. saucepot; set aside. Finely chop unpeeled rhubarb. Place in 2-qt. saucepan. Add 1/2 cup water. Bring to boil. Reduce heat; cover and simmer 2 min. or until rhubarb is soft. Measure exactly 1-3/4 cups prepared rhubarb into saucepot with strawberries; mix well.
Stir sugar into fruit mixture in saucepot. Add butter to reduce foaming. Bring mixture to full rolling boil (boil that doesn't stop bubbling when stirred) on high heat, stirring constantly. Stir in pectin. Return to full rolling boil and boil 1 min., stirring constantly. Remove from heat. Skim off any foam with metal spoon.
Ladle immediately into prepared jars, filling to within 1/4 inch of tops. Wipe jar rims and threads. Cover with two-piece lids. Screw bands tightly. Place jars on elevated rack in canner. Lower rack into canner. Water must cover jars by 1 to 2 inches; add boiling water, if necessary. Cover; bring water to gentle boil. Process 10 min. Remove jars and place upright on towel to cool completely. After jars cool, check seals by pressing middles of lids with finger. (If lids spring back, lids are not sealed and refrigeration is necessary.)