How to Make It
Combine strawberries, sugar, water, pectin, vinegar, and salt in a large saucepan over medium-high; bring to a boil. Cook, stirring occasionally for 6 minutes. Reduce heat to medium; cook, stirring occasionally, until berries release their juices and liquid is syrupy, 15 to 20 minutes. Swirl in butter until melted.
Pour into jars and cool completely uncovered, or alternately place lids on jars and process in boiling water to sterilize.