Sweet Potato Gallette with Lemon and Ginger

4 Tablespoons butter, melted in small pan
1/2 cup tapioca flour
3 Tablespoons brown sugar
2 teaspoons grate fresh ginger
2 teaspoons lemon zest
4 Tablespoons lemon juice
3 large sweet potatoes, peeled, sliced thin
1 lemon, cut in wedges

1) Melt butter in heavy medium saucepan over medium heat. Add brown sugar, ginger, lemon peel and salt; stir until sugar dissolves, about 4 minutes. Keep warm.

2) Position rack in top third of oven and preheat to 400°F. Preheat a 12 inch iron skillet, then add butter generously. Toss sweet potatoes with tapioca flour in large bowl. Add brown sugar mixture; stir to coat potatoes and yams. Arrange sweet potatoes and yams alternately in overlapping circles in prepared skillet.  Spoon any remaining brown sugar mixture over potatoes. Press on potatoes to compact. Cover with lid.

3)    Bake potatoes until just tender, about 1 hour. Uncover and press potatoes with metal spatula to compact. Continue baking until potatoes are very tender, pressing on potatoes occasionally, about 30 minutes longer.