Place all sauce ingredients in a small pot and heat over medium until lightly simmering and bubbly (about 6-8 minutes). Remove from heat, transfer to a small bowl and allow to cool completely. Refrigerate for an hour, if you have the time (recommended).
Prepare the whipped cream:
In a large bowl, beat the heavy cream with an electric mixer on medium until the cream begins to thicken (if preparing the whipped cream a stand mixer, use the whisk attachment). Add the sugar and vanilla and continue beating the cream until soft peaks form when you lift the beaters (or whisk) from the whipped cream.*
Assemble:
Gently fold 1/2 cup of the cooled sauce into the whipped cream a few turns. Add another 1/2 cup and continue folding until the whipped cream is streaked to your liking with the blueberry sauce.
Spoon into parfait glasses. Divide the remaining blueberry sauce as a topping on the whipped cream. Serve immediately or refrigerate for use later the same day.
Notes
*Note: this is my quirky preference entirely, but I actually continue whipping the cream until it's juuuust on the edge of moving into butter territory (for whipped cream experts, this is when the cream becomes spoonably thick, almost spongy - just before it starts breaking down into the globs and crags that lead to butter, but still bright white). When refrigerated, the result is almost soft serve ice cream, only lighter and airier. Irresistible.