For topping: Process the pecans, sugar, and brown sugar in a food processor until the nuts are well chopped. Add the flour and salt. Pulse briefly, to mix. Scatter the cold butter over the mixture and pulse five or six times, until the mixture resembles coarse crumbs. Do not overprocess. Transfer the mixture to a bowl and gently rub it between your fingers until the texture is uniform. Refrigerate the topping.
After the pie has baked for 30 minutes, remove it from the oven and spread the crumb mixture evenly over the top. Tamp the crumb mixture gently, to even it out. Reduce the oven to 375ºF. Bake the pie for 30 to 35 minutes more, until the topping is nicely browned and any visible juices bubble thickly. Transfer the pie to a rack to cool. Serve warm or at room temperature, with some of the caramel sauce drizzled on top. Vanilla ice cream is in order here, too.