For the dough: In a large bowl, whisk together the flour and kosher salt. Using a box grater, coarsely grate the frozen butter, then add it to the flour mixture and toss to coat. Add the water and vodka and hand-knead the mixture until a shaggy dough forms. Cover the dough with plastic wrap and refrigerate for 1 hour.
For the filling and assembly: For the filling and assembly: In a medium bowl, stir together the cream cheese, capers, lemon zest, 1 teaspoon of the kosher salt and the scallions until incorporated.
For the Everything Bagel Seasoning: In a small airtight container, mix together the sesame seeds, poppy seeds, garlic, onion, salt and pepper to combine. Store at room temperature for up to a month. Makes about 1 cup.
Preheat oven to 400° F. Preheat pizza stone or baking steel while preheating oven for a super-crisp and golden-brown crust. Line a half sheet pan with parchment paper.
On a lightly floured surface, roll out the dough into an 18-inch round, ⅙-inch thick. Transfer the dough to the prepared sheet pan. Spread the cream cheese mixture over the dough in an even layer, leaving a 2-inch border. Layer the smoked salmon over the cream cheese, followed by the tomato slices, shingling them to cover the cream cheese. Season the tomatoes with the remaining ½ teaspoon kosher salt.
Fold the exposed border of the dough over the tomatoes with a series of pleats, then brush the outside of the dough liberally with the beaten egg and sprinkle with the everything bagel seasoning.
Bake for 50 to 60 minutes, until the crust is golden brown. Let cool for about 15 minutes, until just warm.
Top the galette with a pinch of flaky sea salt, sliced scallions and dill. Slice and serve.