In a medium saucepan, combine 2 cups of blueberries, sugar, water, and the lemon zest and juice.
Bring to a boil over medium heat, then reduce the heat to maintain a steady simmer. Cook until the berries have burst and the sauce begins to thicken, 8 to 10 minutes.
Remove from the heat and stir in the remaining 1 cup of blueberries. Cool before using.
Notes
Zesting--Use a microplane for zesting your lemon so that you don't have any large pieces of lemon zest in the finished sauce.
Avoid stains--The blueberries will stain wooden spoons, so if you prefer to keep everything stain-free, use a silicone spatula or metal spoon for stirring.
Consistency--The lemon blueberry sauce will thicken slightly as it cools, however, it is a fairly thin sauce, with a consistency similar to syrup.
Storage--Store the sauce in a sealed container or jar in the fridge for up to 2 weeks.
Dietary--This recipe is suitable for gluten-free, dairy-free, and vegan diets.