Scalloped Potatoes & Fennel

Adapted from Bon Appétit, November 2009 {recipe written by Josie Le Balch}
Serves 12

4 cloves of garlic {peeled & smashed}
4 2" long sprigs of fresh rosemary
2 1/4 cup heavy cream
1 teaspoon kosher salt
1/2 teaspoon ground white pepper
2 bulbs fennel {fronds attached}
3 1/2 pounds russet potatoes
4 tablespoons unsalted butter, cut into small pieces

1.  Preheat the oven to 375 degrees.  Grease a 13 x 9 x 2 inch casserole dish with butter.  Scatter the smashed garlic and rosemary sprigs across the bottom of the dish; set aside.
2.  In a large mixing bowl, whisk together the cream, salt and white pepper.  Wash and peel the potatoes {once peeled, place the potatoes into a bowl of water to prevent browning}.  Using a mandoline, or V-slicer, slice the potatoes into 1/8" rounds.  As you work, place the sliced potatoes into the cream mixture and toss to coat. 
3.  Trim the stalks from the fennel bulbs and remove the fronds.  Coarsely chop the fronds; set aside.  Slice the fennel bulbs in half, remove the cores, then slice very thinly on the mandoline {1/16"}.  Arrange half of the fennel slices evenly over the bottom of the casserole.  Remove roughly half of the potatoes from the cream mixture and arrange over the fennel.  Repeat this process once more with the remaining fennel and potatoes.  Pour the cream mixture over the casserole and dot the top with the cubed butter.
4.  Cover the casserole loosely with foil {try to tent the foil slightly so it's not in direct contact with the potatoes} and bake for 1 hour 15 minutes.  Remove the foil, increase the oven temperature to 425 degrees and bake for an additional 15-20 minutes, or until the potatoes are tender when pierced with a fork and the top is deep golden brown in spots.  Let the scalloped potatoes rest for 15 minutes before serving.  If desired, garnish with the chopped fennel fronds.
To Make Ahead: You can bake the scalloped potatoes several hours in advance.   Let them cool completely at room temperature, cover the casserole with plastic wrap and chill until ready to use.  To reheat, preheat the oven to 350 degrees, remove the plastic wrap and cover with foil {use the same foil you originally used, if possible}.  Heat for about 20 minutes, or until heated all the way through.