Serve warm, scooped straight from the casserole dish into bowls. Add ice cream or whipped cream if you like, and don’t be surprised when folks go back for seconds and thirds.
Variations & Tips
If you prefer a slightly less sweet dessert, you can reduce the granulated sugar to 1/3 cup or even 1/4 cup, especially if your blueberries are naturally sweet. For a little tartness, squeeze a tablespoon or two of lemon juice over the frozen berries before adding the sugar, or grate in a bit of lemon zest. A teaspoon of ground cinnamon or a pinch of nutmeg mixed into the dry cake mix gives this a cozy, spiced flavor that feels very Midwestern and homey. You can also swap in a white cake mix instead of yellow, or use a butter-flavor cake mix for extra richness.
If you like a bit of crunch, scatter 1/3 cup chopped pecans or walnuts over the top before baking. For a dairy-free version, use a dairy-free cake mix and substitute melted coconut oil or a neutral vegetable oil for the butter; the flavor will be slightly different but still very good.
Food safety tips: Always bake the dessert until it is piping hot and the juices are actively bubbling; this ensures the frozen berries are fully heated through. Handle the hot casserole dish with thick oven mitts and place it on a heat-safe surface to cool. Refrigerate leftovers within 2 hours of baking, and reheat individual portions in the microwave until hot before serving. Do not refreeze the baked dessert once it has thawed and been cooked, as the texture will suffer and quality will decline.
