Preheat oven to 375 degrees.
Place first 5 ingredients in food processor fitted with steel blade; process until mixture resembles coarse crumbs. With machine running, slowly pour in 2 T. ice water; process, adding more ice water if needed, until dough gathers into mass. Remove dough from processor.
Roll dough on lightly floured surface into 13-inch circle. Transfer to 10-inch tart pan with removable bottom; press dough lightly against side of pan. Trim overhang to 1/2 inch, fold down against pan, and pinch lightly to make sturdy edge 1/4-inch taller than pan. Prick bottom with fork at 1-inch intervals. Refrigerate 1 hour.
Bake tart shell until surface feels dry, 16-17 minutes. Cool completely on wire rack before filling.
Meanwhile, fry bacon in heavy medium skillet over medium-low heat just until crisp and lightly browned, about 6 ninutes. Remove with slotted spoon to paper towels to drain, then crumble.
Pour off all but 1 T. of the bacon fat. Add leeks and saute over medium heat until golden brown, about 10 minutes. Let stand.
Whisk cream, eggs, egg yolk, salt, and pepper in mixing bowl until thoroughly blended.
Place cooled tart shell on baking sheet. Scatter bacon, leeks, and cheese evenly over shell. Place baking sheet on rack in oven. Carefully pour custard into shell.
Bake just until custard is set in center, 25-30 minutes. Let cool at least 15 minutes before serving. Serve warm or at room temperature.