Mix the cornflour with a little extra wine. Heat the jam with the wine and cinnamon until it boils. Stir in the blueberries, then as soon as the sauce boils again, stir in the cornflour mixed with wine, and cook until thickened.
If you want a sharper sauce to accompany meat, stir in 2 tsp smooth or grainy mustard and/or 1 – 2 tsp wine vinegar.