1Blend sweetened condensed milk and egg yolks together. Gradually add lemon juice, stirring until mixture thickens and is well blended. Gently fold in blueberries. Pour filling into baked pie shells.
2In another bowl, beat room temperature egg whites with cream of tartar until foamy. Gradually add sugar, and continue beating until egg whites are stiff. Carefully spread meringue over filling, sealing the edges.
3Bake at 400 degrees F (200 degrees C) until meringue browns, about 6 minutes. Cool. Refrigerate uneaten portions.