Everything Bagel Quiche

Pulse poppy seeds, sesame seeds, garlic flakes, onion flakes, kosher salt, sugar, and 2 cups flour in a food processor a few times to combine. Add butter and pulse until mixture resembles coarse meal with some pieces of butter still visible. With the motor running, drizzle in 7 Tbsp. ice water and continue to pulse, adding another tablespoonful of water if needed, until dough is still crumbly but just holds together when squeezed.

Turn out dough onto a clean surface and knead a couple of times, pressing to incorporate any shaggy pieces. Press into a 6"-diameter disk and smooth out any cracks around the perimeter. Wrap tightly in plastic and chill at least 1 hour.

If chilling more than 1 hour, let dough sit at room temperature 5–10 minutes to soften slightly. Roll out dough on a lightly floured surface to a 14" round. Wrap dough around rolling pin and transfer to pie dish. Unfurl dough from around pin and lift up edges, letting dough slump down into dish. Gently press dough into corners, if needed. Trim, leaving about a 1" overhang. Fold overhang under and crimp edges. Chill 30 minutes.

Place a rack in middle of oven; preheat to 350°. Line dough with a double layer of foil, leaving some overhang. Fill with pie weights or dried beans. Press foil gently up sides of dough to help support weights (no foil should be touching the crimped edges). Bake crust until edges are dry and just beginning to brown, 25–30 minutes. Carefully remove foil and weights. Continue to bake until surface of crust looks dry and the center is just beginning to take on color, 15–20 minutes (you want the crust to stay fairly blond as it will continue to brown when you bake the filling). Transfer to a wire rack and let cool.

Do Ahead: Dough can be made 3 days ahead. Keep chilled, or freeze up to 2 months.

Preheat oven to 300°. Vigorously whisk eggs, heavy cream, sour cream, kosher salt, and pepper in a large bowl to combine. Add scallions and whisk again just to incorporate.

Place pie dish on a rimmed baking sheet. Pour egg mixture into crust. Bake quiche until filling is just set (it will still jiggle a little in the center) and slightly puffed around the edges and crust is golden brown, 80–90 minutes. Transfer quiche to a wire rack and let cool.

Place onion in a fine-mesh sieve and rinse under cold running water. Pat dry with paper towels and place in a medium bowl. Add dill, capers, and lemon juice and toss to combine.

Top quiche with onion mixture and sprinkle with sea salt. Serve with smoked salmon (if using) and lemon wedges.

Do Ahead: Quiche (without toppings) can be baked 1 day ahead. Wrap with plastic or foil and chill. Let come to room temperature before serving.