Preheat oven to 425degrees. Unroll pastry sheet onto a lightly floured surface, roll to a 12-in. circle. Transfer to a 9-in. deep-dish pie plate; trim and flute edge. Refrigerate while preparing filling., In a large skillet, heat butter over medium-high heat; saute onion, mushrooms, broccoli and peppers until mushrooms are lightly browned, 6-8 minutes. Cool slightly., Whisk together eggs, cream and salt and pepper. Sprinkle 1/2 cup cheese over crust; top with spinach and vegetable mixture. Sprinkle with remaining cheese. Pour in egg mixture., Bake on a lower oven rack 15 minutes. Reduce oven setting to 350degrees; bake until a knife inserted in the center comes out clean, 25-30 minutes. (Cover edge loosely with foil if necessary to prevent overbrowning.) Let stand 10 minutes before cutting.