Preheat the oven to 350 degrees Fahrenheit. Lightly grease a 9" pie pan, and evenly sprinkle ingredients along the bottom of the pan. Blend 2 cups milk, 1 cup shredded cheese, 4 eggs, 1/2 cup Bisquick for 1 minute. Pour into pie pan and bake for 50 to 55 minutes.
Optional ingredients can be frozen spinach (thawed and well drained), shredded cheese, tomato, onion, mushrooms or nearly any combination you wish. When baking, rotate the pie pan 180 degrees halfway through the baking process to ensure even browning. Due to varying oven baking times, test for doneness at the halfway point (halfway through the baking cycle described above) by taking a clean knife and inserting it in the center of the quiche and quickly removing it. If the knife comes out clean, the egg/milk/Bisquick mixture has set properly and the quiche is cooked. Remove the quiche from oven and let it stand for 10 minutes to cool. When cooled slightly, slice the quiche into eight even slices. It's important to cool the quiche before slicing because it's difficult to slice when very hot and slices will likely "close up" again as the quiche cools to room temperature. Serve immediately and refrigerate leftovers.