Step 1

Preheat oven to 350°F. Coat an 8-inch-square baking pan with cooking spray.

Step 2

Stir graham cracker crumbs, butter, sugar and half the zest together in a medium bowl. Press the mixture firmly and evenly into the prepared pan. Bake until lightly browned around the edges, about 10 minutes. Let cool in the pan on a wire rack for at least 10 minutes.

Step 3

Meanwhile, thoroughly whisk condensed milk, lemon juice, egg and the remaining zest together in a medium bowl. Stir in blueberries. Pour the filling evenly over the baked crust. Bake until set, 16 to 18 minutes. Let cool at room temperature for 1 hour. Cover and refrigerate for at least 1 hour more.