Meanwhile, make the blueberry sauce: Whisk the water, lemon juice, orange blossom water, and cornstarch together in a medium saucepan until the cornstarch has dissolved. Stir in the blueberries and sugar and bring just to a simmer over medium-high heat. Reduce the heat to medium-low and cook, stirring occasionally, until the blueberries begin to soften and the sauce thickens slightly, about 5 minutes. Taste and adjust the seasoning, adding more orange blossom water and/or lemon juice, if desired. Remove from the heat and set aside; if desired, reheat the sauce over low heat before serving. (The sauce can be made up to 5 days ahead, cooled, and refrigerated in a sealed container. Bring to room temperature or reheat gently before serving.)