To make the blueberry sauce, mix together the blueberries, lemon zest and juice, 1/3 cup sugar in a small sauce pan over medium heat.

Once the mixture starts to bubble, you'll see some liquid from the blueberries. Take about 1/4 cup of the juice and mix it with the corn starch to make a slurry, getting out all lumps. Quickly mix it back into the blueberry sauce.

You should almost immediately see that sauce start to thicken. Remove from heat, give it a quick stir for good measure, and transfer to a jar (you can sterilize the jar and then can it, but I only made this one batch so I don't need to can it).

Cut up some blueberries, and pour a little blueberry sauce on top.