4 Onions (2 red, 2 yellow) – Cut in ½ and then sliced paper thin
3 ½ tbsp Butter
1 ½ tsp Bacon Fat (or EVOO)
2 Large Garlic Cloves – Peeled, smashed into a paste
3 Large Russet Potatoes – Peeled and sliced about 1/8” (I use a Mandolin)
1 tsp Salt
¾ tsp Pepper
1 tsp Fresh Thyme (or ½ tsp dried)
2 tbsp Parmesan Cheese
2 Cups Beef Broth
In large pan over med. heat, add 1 ½ tbsp butter, the bacon fat and add onions. Sautee for about 25 minutes or until translucent and starting to caramelize. Add in garlic and sautee for about another 5-10 minutes.
Butter a baking dish, bottom and sides with 1 tbsp butter (I used one that was about 10x7 but you can use any similar size). Take 1/3 of the onions and add a layer to the dish. Take potatoes and create 2 layers with each slice overlapping the previous one. Sprinkle 1/3 salt, 1/3 pepper, 1/3 parm cheese and 1/3 thyme over potatoes. Repeat onions, potatoes and seasoning 2 more times. Add 2 cups beef broth. Break 1 tbsp butter over the top of the potatoes.
Cover dish with aluminum foil and place in preheated 350 degree oven for 2 hours. (I put my dish on a cookie sheet just in case there was any spill over.) Take foil off and cook another ½ hour to let the top layer of potatoes brown and crisp. Test with a knife to make sure potatoes are fully cooked. Let rest for at least 15 minutes before you cut into it to let the beef broth soak into the potatoes.
* You could add shredded cheese in between the layers and on top for a variation.