Heat oven to 425 degrees F. Unfold prepared piecrust into 9-1/2 x 1-inch tart pan with removable bottom; prick bottom with fork. Line with foil; fill foil with beans or pie weights.
Bake crust in 425 degree F oven 10 minutes. Remove foil and pie weights. Bake crust another 10 minutes.
Meanwhile, in large skillet, melt butter over medium-high heat. Add parsnips, carrots, scallions and salt; cover and cook, stirring occasionally, until softened, about 8 minutes. Remove from heat.
Reduce oven temperature to 375 degrees F. Sprinkle 3/4 cup of shredded cheese over bottom of prepared pie crust. Spread parsnip-carrot mixture on top.
In large measuring cup or medium-size bowl, beat together eggs, cream, cumin, cayenne and nutmeg until blended. Pour over parsnip-carrot layer. Sprinkle with remaining 1/4 cup cheese.
Bake tart in 375 degree F oven until knife inserted in center comes out clean, about 25 minutes. With sharp knife, carefully release edge of tart from pan. Remove side of pan; place tart on serving plate. Serve warm or chilled. Makes 8 servings.