In a large mixing bowl, mash the strawberrries with a potato masher or pastry cutter. Transfer the mashed strawberries to a large, non-reactive pot with the chopped rhubarb, split vanilla bean, and 1 cup of the sugar. Stir thoroughly to draw out some of the liquid.

Cook over medium low heat, stirring frequently, until the rhubarb and strawberries have broken down, about 30 minutes to an hour. Reduce the heat to low, and simmer for 1-2 hours, stirring occasionally, until the fruit has reduced to about half of its original volume, and has reached a fruit butter consistency. The total time that this process will take varies a great deal depending one the amount of water in the fruit. Taste and adjust the sugar if neccessary, adding up to an additional 1/2 cup of sugar. Cook, stirring, until the sugar has dissolved. Remove from heat, and discard the vanilla bean segments.

Fill a pot large enough to hold 4 half-pint jars with water and set over high heat to boil. 

With a funnel and small ladle, fill sterilized jars with the strawberry rhubarb butter, wipe the rims with a clean damp cloth, and apply sterilized lids and bands. (See note.) Submerge the filled jars in boiling water, and process for 15 minutes. Remove from the pot, and set aside to cool. When cool enough to handle, remove the ring and check the seals. 

Stored in a cool, dark place, this is good for 6-9 months. However, this is good to eat right away!