In a small saucepan, add water and sugar and slowly heat until sugar dissolves. Slowly whisk in corn starch to thicken. Add 1 cup of the blueberries and continue stirring on medium to high heat until blueberries begin to pop and mixture begins to thicken. Once mixture begins to thicken, add 2nd cup of blueberries and butter and continue to stir for a couple of minutes. Turn heat down to low and simmer for another minute. Towards the end, add the lemon zest for freshness and stir into mixture. Serve this warm blueberry sauce with my french toast souffle, pancakes, waffles, pound cake or ice cream.