The pan that can, did it again

It's amazing what you can throw together in a 9x13" pan, and to prove the point, I dipped into my book 9x13: The Pan That Can again. You know me well enough by now to know that there is nothing I like better than a one-dish meal, where all you need to do is put together a salad, and dinner is sorted. This dish therefore fit the bill admirably, and, fanfare please, was gobbled up (noisily and rudely, obviously) by all three children. Honestly, cheese, ham and potatoes - what's not to like. I do realize that I risk the wrath of any Brits reading, because I'm not sure you can get shredded hash brown potatoes there - but you could easily substitute with some par-boiled potatoes which you then shred in the food processor and leave to drain a little (so that they are not too wet). More time-consuming yes, for which I apologize profusely! It isn't my fault that I live in the land of complete and utter convenience food!

Ham and Potatoes Au Gratin
Serves 6+

3 TBSP butter
3 TBSP AP/plain flour
1 3/4 cups milk
2 eggs, slightly beaten
1 1/2 cups shredded/grated cheddar cheese
1 TBSP Dijon mustard
1/4 tsp black pepper
2 TBSP olive oil
2 small onions, sliced
1 10oz package of frozen chopped spinach, thawed and squeezed dry
12 oz cooked ham, cut  into bite-size strips
1 20oz package of frozen shredded hash brown potatoes, thawed.
1/4 cup shredded/grated parmesan

1. Preheat oven to 350 degrees F (180 C).
2. In a medium saucepan, melt butter over medium heat, then stir in flour. Add milk, and cook and stir until thickened and bubbly. Let it bubble over a low heat for one minute more.
3. Remove from heat, and stir 1 cup of the sauce into the beaten eggs. Return the egg mixture to the pan and stir in cheddar cheese, mustard and pepper until cheese melts. Set aside.
4. In a large skillet, heat olive oil and cook onions over medium heat until tender. Stir in spinach, then set aside.
5. Spread half of the ham in an ungreased 9x13" pan or baking dish. Sprinkle half of hash browns over ham. Spoon half of the cheese sauce over the hash browns and gently spread it evenly over dish. Spoon half of the spinach mixture over this. Then repeat the layers with the remaining ham, potatoes, sauce and vegetables. Finally sprinkle with parmesan cheese.
6. Bake uncovered for 30 minutes or until heated through. Let stand for 10 minutes before serving.