Start by preheating the oven to 350°F. Coat a 3-qt. baking dish with nonstick spray.
Spread lemon pie filling across the bottom of the baking dish. Then top with blueberries.
Sprinkle the cake mix over the lemon-blueberry mixture. Top with poppy seeds (if you are using them). Place butter slices evenly over cake mix.
Bake for 35 to 40 minutes or until browned. Cool for 15 minutes before serving. Top servings with additional blueberries, whipped cream, or ice cream.
