Roll out pastry dough and line 1-inch fluted tart shell. Freeze about 30 minutes. Bake at 400 degrees F 10 to 12 minutes or until golden brown.
For roasted potatoes: Peel and thinly slice potatoes. Toss potatoes with melted butter, rosemary and salt and pepper to taste. Line baking sheet with parchment paper. Spread potatoes on parchment. Bake at 350°F 30 minutes or until tender and just beginning to turn golden.
Meanwhile sauté leek in butter in small skillet until tender. Season to taste with salt and pepper.
For custard: Whisk eggs, yolks, cream, milk, salt, pepper and nutmeg until thoroughly mixed.
Sprinkle Fontina cheese and sauteed leek over bottom of baked tart shell. Layer potatoes over leek in concentric circles. Pour custard mixture over potatoes. Bake at 350°F 30 to 40 minutes or until custard is puffy around edges and knife blade inserted near center comes out clean.
Cool slightly and slice into six pieces. Garnish with fresh rosemary.