Upside down potato and onion tart

I love potatoes and I love onions.  This recipe puts them both together--perfect!  I got this recipe from Hizzoners Deli.  I used the basic idea, but totally made this recipe my own-it wasn't too hard to do.  I also stopped taking pictures of my food during this recipe.  That didn't last long :/

Ingredients:
-2 1/2 tablespoons butter (I used stick butter and did not want to cut 1/2 a tablespoon, so I used 3 tablespoons)
-12 sprigs thyme, strip the leaves from the stems (I really want to start an herb garden, but the only "herb" I have is catnip and I think I've killed it!  So I just sprinkled some dried thyme in the butter)
-1 large onion, sliced somewhat thickly
-1 lb potatoes, washed and thinly sliced (I used Klondike golden potatoes.  I didn't peel them, I just washed them really well.  As my family knows, I am terrible at thinly slicing anything, so I used my cheese grater and it worked really well.  Just a word of caution, the potato gets really slick and you have to be careful not to slice your fingers.  Also, I didn't know how much was a pound of potatoes.  So I just guesstimated)
-2 tablespoons olive oil
-1/2 cup grated gruyere (I had no idea what this was--so I looked it up and found out it was cheese.  I just used extra cheese that is listed below.  I knew what those were)
-1/2 cup crumbled feta
-1 cup grated mozzarella
-salt and pepper to taste

Steps: (Now this is where I vary from original recipe.  If you want that, follow the above link.  That allows you to see why it is called upside down potato and onion tart.  But I didn't have an oven proof big skillet, so I just used a 9 X 13 glass pan. It worked just fine)
1. Preheat oven to 400 degrees
2. Melt the butter in a skillet over medium heat
3. Add the thyme and onion and cook for 5 minutes (I love the smell of cooked onions)

4. Place the potatoes, oil, cheeses, salt, and pepper in a bowl and toss to combine.  (Next time I will add more spices.  The potatoes were slightly bland.  You just have to experiment with whatever spices you like best)
5. Put the onions on the bottom of the 9 X 13 pan, pour the potato mixture on top
6. Bake for 45 minutes or until golden brown and cooked through.  (The original recipe didn't state covered or uncovered, so I did 15 minutes covered, 30 uncovered.)

Overall, I liked this recipe and will make it again.  Changes will include spicing it up more.  I will also use more onion.  Finally, I will cook it longer--I did not cook the potatoes long enough and they were still "raw tasting".   I would also probably use more cheese.  I really like feta cheese and could use more in the potatoes.

Up next: Pork Chops