In a small saucepan set over medium-high heat, combine 3/4 cup blueberries, sugar, vinegar, cornstarch and cinnamon; bring to a boil. Reduce heat to medium and cook for 5 to 8 minutes or until thickened. Fold in remaining blueberries. Let cool completely.
Preheat oven to 350˚F. Grease 9-inch square baking pan with butter. Line bottom and sides of pan with enough parchment paper to overhang edges. Using electric mixer, beat cream cheese with sugar until light and fluffy; beat in egg. Add cream and vanilla and beat until well combined; set aside.
In a heatproof bowl set over larger pot of barely simmering water, melt butter and chocolate, stirring occasionally. Remove from heat. Stir in sugar, cocoa powder and salt. Let cool slightly. Stir in eggs, one at a time, until well combined. Stir in flour. Scrape into prepared pan; smooth top.
Can be wrapped and refrigerated for up to 4 days or frozen for up to 1 month.