Preheat oven to 350F (180C)
Put the tart form in the freezer. Roll the pastry dough quickly between 2 pieces of parchment paper until it is the right size for the tart form. Put the rolled dough into the freezer for 5 minutes.
Transfer the cold rolled dough into the cold tart form, patching where necessary. If the dough gets too sticky, put it back in the freezer for 5 minutes. Brush with the whisked egg.
Cover the crust with parchment paper and fill with ceramic pie weights or beans. (I didn't have any beans so I used barley....worked great!) Bake for 15 minutes in the oven until slightly browned. (Keep a close eye on the crust while baking, it can quickly get too browned!) Take out, remove the pie weights and parchment paper and let cool on a rack.
While the crust is baking, fry the bacon and onion on high heat until brown, not completely crispy. Drain on paper towels.
Cut ⅔ of the cheese into small cubes. Finely grate the last ⅓ of the cheese.
Whisk the Sour cream, whipping cream, eggs and spices together in a small bowl.
Put the baked crust onto your oven baking rack or shelf. Arrange the bacon, onion and cheese cubes in the bottom of the pie crust. Pour over the cream mixture and top with the shredded cheese. Carefully transfer the pie into the oven.
Bake (350F / 180 C) for 25-30 minutes turning halfway through until golden brown, the center should still be a bit soft. Let stand 5 minutes before transferring to serving plate.