On a lightly floured surface, roll pie crust into a 13 inch circle. Transfer to pie/tart pan and take special care to press in the sides and bottom. Bake the crust until it is golden. Set aside. Set oven to 375°F.

Heat olive oil and butter in a skillet over medium heat. Add sliced mushrooms and shallots; season with salt and pepper. Cook, stirring often, until shallots are soft. Let cool slightly, then spread evenly over bottom of tart crust. Add tomatoes and white parts of scallions.

Combine the eggs, heavy cream, cheese, basil in a medium bowl. Season with salt and pepper. Then pour over vegetables.

Bake tart until edges of crust are golden brown and filling is set, about 20- 25 minutes. Let cool in pan for at least 15 minutes.

To serve: Remove tart from pan. Tart can be eaten warm or at room temperature.