1. Heat grill to medium-high. Brush corn, tomatoes and scallions with oil and place on grill. Grill corn 8 to 10 minutes, until lightly charred, turning often. Meanwhile, grill tomatoes and scallions about 3 minutes, turning once until lightly charred. Chop tomatoes and scallions; cut kernels from cob.
2. Heat oven to 450 degrees . On a well-floured surface, roll crust into a 17 x 7-inch rectangle and fit into a 131/2 x 41/2-inch rectangular tart pan with removable bottom. Prick bottom and sides of crust with fork. Line with foil; fill with pie weights or dry beans.
3. Bake at 450 degrees for 10 minutes. Remove from oven, remove foil and weights, and lower temperature to 350 degrees .
4. Toss together Havarti, corn, tomatoes and scallions; season with salt. Scatter over bottom of tart. Whisk together eggs, egg yolk, cream and mustard. Pour over corn and tomato mixture.
5. Place tart pan on a baking sheet. Bake at 350 degrees for 55 to 65 minutes or until a knife inserted near center comes out clean. Remove to a wire rack and cool 15 minutes before removing side of tart pan.Piecrust
6. In the bowl of a food processor, pulse 1 1/4 cups all-purpose flour and 1/2 tsp salt until combined. Add 1/4 cup (1/2 stick) wellchilled unsalted butter, cut into small pieces, and 1/4 cup well-chilled vegetable shortening, cut into pieces. Pulse a few times until mixture resembles coarse cornmeal. Gradually add 4 tbsp cold water while pulsing. Pulse until mixture just begins to come together. Form into a ball and flatten into a disk. Wrap tightly in plastic and chill for at least 1 hour.Note:
7. If using for Rustic Grilled Vegetable Tart, form into a rectangular shape before chilling.