CORNMEAL PASTRY: In bowl, mix together flour, cornmeal, sugar and salt; using pastry blender or 2 knives, cut in butter until large crumbs.
Whisk sour cream with water; drizzle over flour mixture, tossing with fork until dough comes together, adding up to 1 tablespoons more water if necesary. Wrap and refrigerate until chilled, about 1 hour.
On lightly floured surface, roll out pastry to scant 1/4-inch thickness; fit into 9-inch quiche dish or pie plate. Fold edge under, leaving 1/4-inch above rim; flute or crimp edge with fork. Prick all over with fork. Refrigererate for 30 minutes.
Line pie shell with foil; fill with pie weights or dried beans. Bake in bottom third of 400F oven until rim is light golden, about 20 minutes. Remove weights and foil; bake for 10 minutes. Let cool on rack.
In large skillet, cook bacon over medium-high heat until crisp, about 5 minutes. Drain on paper towels. Drain fat from pan.
In same pan, heat oil over medium heat; cook onion, corn, pepper, salt and thyme over medium heat, stirring occasionally, until onion is softened, about 5 minutes. Set aside.
In large bowl, whisk together eggs, milk and cream. Crumble bacon and add to egg mixture along with corn mixture. Sprinkle cheese over pastry shell. Pour in egg mixture.
Shielding pastry rim with foil, bake in 375F oven until knife inserted in center comes out clean, about 40 minutes. Let cool on rack for 10 minutes.