An easy homemade strawberry-rhubarb jam that's thousands of times better than anything you'll find at the grocery store.
Mash the strawberries and combine with the rhubarb to measure 5 total cups. Add the fruit and the fruit pectin to a large deep pot, stir, and bring to a rapid boil, stirring frequently. (The boil should be strong enough that it continues even while you are stirring.) Add the sugar and butter and stir to combine. Bring once again to a rapid boil, stirring frequently. When the mixture is at a full roiling boil, let it boil for exactly one minute. Remove from heat and ladle into prepared jars. Wipe the mouth of the jars clean, put the lids on and screw on the bands (but not tightly). Process jars in boiling water or according to your canning bath directions. The lids should pop to seal. Keep sealed jam jars in a cool, dry place for up to one year. Refrigerate jam once it is opened.