In medium saucepan, stir sugar and cornstarch together with a whisk, then stir in water until smooth. Stir in blackberries.
Place pot on heat and bring to boil stirring frequently. Bring to a boil and crush until the seeds have been released from the berries.Once sauce thickens, it's done! If you want a thicker syup add a little more cornstarch.
Remove from the heat, add the vanilla extract and stir. Carefully strain the blackberry mixture through a mesh strainer. Serve immediately over pancakes or waffles.
IF CANNING: Pour the hot syrup into sterilized jars leaving 1/4 inch headspace, wipe the rims with a damp cloth and screw on the lids. Process in a water bath, 10 minutes for pints and 15 minutes for quarts. Carefully remove and let the jars rest undisturbed for 24 hours.