Yes, in fact, you can mix up the batter and the topping, throw it all together according to the recipe; then cover your baking dish and place it in the fridge 'til you're ready to bake it the next morning. If you're actually baking it ahead of time, I would recommend baking it no more than 1 day in advance. Then just cover it and store it on the counter 'til you're ready to serve it.