The first step is to get those onions caramelizing! Melt the butter in a small saucepan, and then add the thinly sliced onions. Mix to coat them all with butter. Place the lid on the saucepan, and cook for about 45 minutes on the lowest possible heat. Open up and stir frequently to stop them from overcooking at the bottom or sticking to the pan.
Meanwhile, you can prepare a homemade enchilada sauce if that's what you've decided to do, grate all of your cheese, and prepare any side dishes and toppings for your meal. (Some suggestions and recipe links are in the blog post!)
Once the onions are soft, sticky and sweet, transfer them to a bowl and leave them to cool for a few minutes.
Add the feta cheese to the onions and mix through, followed by the mozzarella and cheddar, to complete your filling.
Heat the oven to 200C / 400F while you assemble your enchiladas.
Grease a medium casserole dish and then pour a layer of enchilada sauce over the bottom.
Grab a tortilla, smear some enchilada sauce over the inside, spoon in your filling, and roll. Place in the dish on top of the sauce.
You will get around 12 enchiladas if using 6 inch (15cm) tortillas, less if yours are larger.
Once your enchiladas are all assembled, pour more sauce over the top to completely cover them.
Cover the pan and place in the oven for 20 minutes.
Bake for 20 mins at 200C
Remove from the oven and top with some additional crumbled fresh feta and fresh, chopped cilantro (coriander).