Pastry

Put flour and salt in large bowl; toss with fork. Make well in center; fill with oil and water. Blend briefly with fork, then - using wide, sweeping strokes - stir briskly, until evenly mixed. Dough will be dampish and oily.

Put dough on large piece of plastic. flatten into 3/4-inch disk; wrap in plastic. Let rest 10 minutes before using. Grease 9 1/2-inch deep-dish pie pan. Preheat oven to 400F.

Roll pastry into 12-inch circle between two sheets of wax paper or plastic wrap. Peel off top sheet; invert pastry over pie pan. Peel off second sheet, then tuck pastry into pan without stretching it, pinching overhang into an edge. Chill 15 minutes. Smooth sheet of aluminum foil over pastry (it should fit like a glove); fill with dried beans or rice. Bake 20 minutes. Remove pan from oven; lift foil with beans from pan. Using fork pierce pastry 6 to 8 times. Rduce oven to 375F, and bake 7minutes. Cool on wire rack. Leave oven on.

Filling

Heat oil in large skillet over medium heat. Add onion, and cool, stirring, 5 minutes. Add muchrooms; cover, and cook 3 to 4 minutes, stirring occasionally. Stir in spinach and garlic; cover, and cook 2 to 3 minutes, or until spinach is wilted.

Lightly whisk eggs in mixing bowl. Whisk in milk, mustard, pepper and salt.

Sprinkle 1/4 cup grated cheese over bottom of pastry. Bake 2 to 3 minutes to melt cheese.

Spread vegetable mixture in pastry shell. Sprinkle with half of remaining cheese. Slowly pour in egg mixture, then sprinkle with remaining cheese. Bake 40 to 45 minutes, or until golden brown and slightly puffy. Transfer to wire rack, and let cool 15 minutes before serving.