Preheat your oven to 350°F. Grease a 9×13 inch baking dish with butter or nonstick spray.
Spread the blueberry pie filling evenly in the bottom of the prepared dish. Sprinkle the blueberries over the top. Drizzle with lemon juice and sprinkle with lemon zest.
Sprinkle the dry lemon cake mix evenly over the fruit layer. Do not mix it in.
Arrange the butter slices evenly across the top of the dry cake mix, covering as much surface area as possible.
Bake for 45–50 minutes or until the top is golden and the filling is bubbly around the edges.
Cool slightly before serving. Enjoy warm on its own or with whipped cream or vanilla ice cream.
Notes
No fresh blueberries? You can skip them or use more pie filling instead or use frozen blueberries. You don’t need to thaw them.
Try a variation with a white or yellow cake mix if you don’t have lemon cake mix.
Butter coverage matters! Make sure the butter covers most of the cake mix to avoid dry spots. If you cut the butter too thick, you may need to use more than the recipe calls for.