Fennel-Potato Gratin

This is the dish I brought to Thanksgiving pot-luck and was told it was the best dish that night! It's a simple casserole dish that is perfect for pot lucks and goes great with chicken too.

3 Lbs Yukon Gold potatoes, thinly sliced
2 fennel bulbs, thinly sliced
4 cups heavy cream
2 Tbsp butter
2 Tbsp flour
1 tsp nutmeg
pinch white pepper
salt to taste

Preheat oven to 350F.
Slice potatoes and fennel about 1/8 inch thick. No need to peel the potatoes. If you have a mandoline, use that but if not, a knife will work just fine.
Meanwhile, make a rue by melting the butter in a sauce pan, add flour and let it come to a bubble. Add heavy cream, nutmeg. white pepper and salt. Bring to boil and reduce heat.
Layer the potatoes on the bottom of a greased casserole dish. Then add a layer of fennel. Pour a small amount of creamy sauce over potatoes and fennel. Continue layering potatoes, fennel and cream to top of casserole dish. Cover dish with parchment and foil and place in oven for aprox. 1 hour or until potatoes are tender.
Raise the temperature of the oven to 425F, remove foil and parchment and bake until top is brown, aprox. 10 minutes. If you want, you can add cheese to the top (Parmesan would work best), place back in oven for 10 to 15 more minutes. Let dish cool for 10 minutes and serve!