To prepare a oven cheese and spinach fondue appetizers recipe, you will first need to prepare the ingredients. Preheat the oven to 375 degrees F (190 degrees C) and prepare your oven rack. Place the cheese, spinach, and garlic in the bottom of an 8-inch (22-centimeter) glass baking dish. Pour the melted butter over the mixture and stir to combine. Set the dish aside until you are ready to serve.