Preheat oven to 375°F (190°C). Line a rimmed baking sheet with foil.

On prepared pan, arrange onion and shallot. Brush with oil, and sprinkle with ½ teaspoon (1.5 grams) salt.

Bake until onion starts to brown slightly, 15 to 18 minutes. Let cool completely. Leave oven on.

Spray a tall-sided 10-inch fluted round removable-bottom tart pan with baking spray with flour.

On a lightly floured surface, roll Thyme and Black Pepper Pâte Brisée into a 14-inch circle. Transfer to prepared pan, pressing into bottom and up sides. Trim edges, if necessary. Freeze until firm, about 20 minutes.

Top prepared crust with a piece of parchment paper. Add pie weights. Place on a baking sheet.

Bake until crust is mostly dry and set, 30 to 35 minutes. Carefully remove parchment and weights, and bake until inside of crust is dry and edges are starting to turn golden brown, about 5 minutes more. Reduce oven temperature to 325°F (170°C).

In a large bowl, whisk together cream, milk, eggs, thyme, rosemary, parsley, pepper, and remaining 1 tablespoon (9 grams) salt until well combined.

Reserve 8 slices of onion and 14 slices of shallot; arrange remaining onion (about 200 grams) and remaining shallot (about 50 grams) in bottom of prepared crust. Place tart pan on a rimmed baking sheet, and place in oven. Quickly but carefully pour cream mixture into crust.

Bake for 35 minutes. Leaving quiche on oven rack, carefully arrange reserved onion and reserved shallot on top of quiche. Bake until set and top is golden, 20 to 30 minutes more. Let cool completely in pan. Remove from pan before serving.