Grease a large baking dish with 1 tbsp butter.
In a large sauté pan over medium-high heat, cook sausage, stirring with a wooden spoon to break the meat into small clumps, until browned, about 10 minutes. Transfer the sausage to a large mixing bowl, leaving the fat in the pan.
Turn the heat down to medium and add the onions to the pan along with 1 tablespoon of butter. Cook the onions, stirring constantly, until soft and lightly caramelized, about 6 minutes.
Add the onions to the mixing bowl with the sausage, along with the bread cubes, grated cheese, apples, parsley and sage.
In a medium bowl, whisk together the Egg Beaters, half-and-half, salt and pepper.
Pour the Egg Beaters mixture evenly over the bread mixture. Cover tightly and refrigerate for at least a few hours or preferably overnight.
Preheat the oven to 350°F. Bake for approximately one hour, uncovered, until puffed and golden brown. Serve immediately.