Set your oven to preheat at 350 degrees Fahrenheit.
Place the grapes on a baking sheet lined with parchment paper.
Roast for 45 to 60 minutes, waiting for the grapes to burst, wrinkle, and shrink to roughly half their size as a rich syrup builds on the tray.
Remove from heat and allow the grapes to reach room temperature completely.
Beat the softened butter for 1-2 minutes until light, smooth, and fluffy.
Fold in the cooled roasted grapes, any caramelized sugars or accumulated juices, cinnamon, and vanilla extract; mix until thoroughly combined.
Pack into an airtight container and chill in the refrigerator until ready to serve.
Give the butter a few moments to soften slightly prior to serving.