Whisk the topping flour, brown sugar, granulated sugar, cinnamon, and salt in a medium bowl, breaking up any compacted brown sugar. Pour in the melted butter and stir with a fork until no dry flour remains and the mixture forms irregular clusters ranging from pea-size to about 1 inch. Do not compress it into one solid mass. Refrigerate the bowl for at least 20 minutes while making the crust; chilling firms the butter so the crumbs retain definition during baking.
Pulse the crust flour, granulated sugar, and salt in a food processor to combine. Add the cold butter and pulse until most pieces are pea-size, with a few larger flakes remaining. Drizzle in 3 tablespoons ice water and pulse briefly; squeeze a handful, and add the final tablespoon only if it will not hold together. Turn the shaggy dough onto the counter, press it into a 1-inch-thick disk without kneading, wrap tightly, and refrigerate for 45 minutes.
Set a rack in the lower third of the oven and heat it to 400°F. Roll the chilled dough on a lightly floured surface into a 12-inch circle, rotating often to prevent sticking. Fit it into a 9-inch metal pie plate without stretching, trim to a 1-inch overhang, fold the edge under, and crimp. Freeze for 15 minutes. Line with crumpled parchment, fill with pie weights, and bake on a preheated rimmed sheet for 15 minutes. Remove the weights and parchment, then bake 5 minutes until the base looks dry and lightly golden.
While the shell blind-bakes, place the quartered strawberries in a large saucepan and crush about one-third of them with a spatula to release juice. Whisk the filling sugar, cornstarch, and salt together, then stir them into the fruit with the lemon juice. Cook over medium heat for 6 to 9 minutes, stirring steadily and scraping the bottom, until the juices reach a full simmer and become glossy and visibly thick. Simmer for 1 minute, remove from the heat, and stir in the vanilla.
Place the partially baked shell, still in its pie plate, on the rimmed baking sheet. Spoon in the hot strawberry filling and spread it evenly without pressing hard against the delicate crust. Break the chilled topping into varied clusters and scatter them over the entire surface, covering the fruit but leaving a few narrow gaps where steam and filling bubbles can escape. If the pastry rim already looks medium golden, shield it loosely with strips of aluminum foil before returning the pie to the oven.
Reduce the oven temperature to 375°F and bake the pie on the lower-third rack for 45 to 55 minutes. Rotate the baking sheet after 30 minutes for even color, handling it gently because the filling is fluid and extremely hot. The pie is done when the crumb topping is deep golden, the exposed pastry is browned, and thick strawberry bubbles rise through openings near the center, not only around the edge. If the topping darkens too quickly, cover it loosely with foil for the remaining time.
Transfer the pie plate to a wire rack and leave the pie uncovered at room temperature for at least 4 hours. Do not refrigerate it while warm or cover it, since trapped condensation softens both the crumb topping and pastry. The filling will look loose immediately after baking but thickens as the cornstarch gel cools. Once completely cool, cut with a sharp knife, wiping the blade between portions, and lift each wedge with a thin pie server. Earlier slicing will produce a warm but runny filling.
