One bag (20 ounces) frozen strawberries can be substituted for fresh. However, they make a slightly less vibrant sauce.
Wash, stem, and hull the strawberries. Cut in half, and quarter if large. In a small saucepan, combine berries and jam. Cook over medium-high heat, stirring occasionally, until the berries have softened and the mixture becomes a sauce, about 5 minutes. Cool sauce before serving or, store in an airtight container in the refrigerator up to 1 week.