Preheat oven to 450°F. To prepare Baked Oil Pastry: In a medium bowl, stir together flour and salt. Add oil and milk all at once. Stir lightly with a fork. Form into a ball. On a lightly floured surface, slightly flatten dough. Roll from center to edge into a circle about 12 inches in diameter. To transfer pastry, wrap it around the rolling pin; unroll pastry into a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch it. Trim pastry ½ inch beyond edge of pie plate; fold under and flute as desired. Line pastry with a double thickness of foil. Bake for 8 minutes. Remove foil. Bake for 5 minutes more. Cool on a wire rack while preparing filling.
Reduce oven temperature to 350°F. Shred Gruyère cheese; you should have ¾ cup. Set aside 2 Tablespoons of the cheese.
To prepare Filling: In a large bowl, beat together remaining cheese, the egg, spinach, half-and-half, thyme, and pepper. Pour egg mixture into prepared crust.
Bake for 40 minutes. Sprinkle with the reserved 2 Tablespoons cheese. If necessary to prevent overbrowning, cover edge of quiche with foil. Bake about 10 minutes more or until a knife inserted near center comes out clean. Let stand on a wire rack for 10 minutes before serving. Cut into 10 slices.