First up, set your oven to 335 degrees and butter your pie dish - I used our 11.5 inch pie pan. If you're using a 9 inch pan, then I suggest you cut this recipe in half.
Once the oven is warming up, dice the onions and sauté them with the garlic and the butter until golden brown. Then, line the pie dish with them.
Up next, time to cook the spinach. I much prefer cooking fresh spinach to using frozen, yet if you have good luck with frozen, then go for it. Cook the spinach until it's soft and wilted, then dish out onto a few paper towels and remove the excess water. Spoon out the spinach into the pie pan, distributing it evenly in the pan. This is when things start to smell delicious!
Once that's done, layer on the crumbled feta cheese and top with the shredded old cheddar. Add salt and pepper to taste. Now, in a bowl, whisk the 10 eggs and the cup of milk. Combine well, yet not too much, and then pour over the onion, spinach, and cheese. At this point, I usually use a fork to gently wiggle various spots back and forth to ensure the egg and milk mixture has made it to the bottom of the pan. No need for perfect layers, though.
Lastly, cut slices of red pepper - you could also use mushrooms or tomatoes, yet they add too much wetness for me. With the slices of red pepper, lay them out on top of the quiche in a pattern that looks good to you.
Then, cook up for 45-55 minutes until the eggs are set and the top of golden brown. Let it cool for about 7-10 minutes, then eat up.