4 cups fresh blueberries, washed, stems picked off
1 cup water
½ cup sugar
1½ tablespoons cornstarch dissolved in 3 tablespoons water
Put 3 cups of the blueberries, water, and sugar in a medium-sized saucepan. Bring to a boil over medium-high heat.
Turn the heat down to low and gently mix in the dissolved cornstarch. Increase the heat, bring to a boil again, then turn down the heat once more to simmer for a few minutes, stirring as needed. The sauce should be nice and thick.
Add the last cup of blueberries to the hot mixture and stir. (Adding this last cup at the very end gives the sauce a lovely texture.) Remove from heat and let cool. Serve at room temperature or refrigerate until ready to serve.