Preheat a panini grill according to manufacturer's directions for sandwiches (or use a large frying pan over medium heat). Butter one side of each slice of bread. Lay two slices of bread in front of you, buttered-side-down. Divide your fillings in half and start stacking the ingredients on both slices, in this order: cheese, spinach, bacon, tomato, onion, cheese; top with second slice of bread. Place sandwiches on the panini grill or in a frying pan. Cook until the fillings are heated through, the bread is an attractive golden colour and the cheese is melted. Remove from heat, allow to sit 3-5 minutes, then cut and serve immediately. Yield: 2 servings.