Whisk the flour, sugar, and salt together. Cut in the cold cubed butter with a pastry cutter or your fingertips until the mixture looks like coarse crumbs with a few pea-sized pieces left.

Add the ice water 1 tablespoon at a time, tossing with a fork, until a squeezed handful just holds together.

Crumble the dough into a 9-inch fluted tart pan with a removable bottom and press it evenly about ¼ inch thick across the base and up the sides. Freeze 20 minutes.

Dock the base with a fork, line with parchment, and fill with pie weights. Bake at 375F for 18 minutes, remove the weights and parchment, and bake 6 to 8 minutes more until pale gold and set. Cool.

Beat the mashed sweet potato on medium 1 minute. Add the eggs, sugar, evaporated milk, flour, vanilla, and cinnamon and beat 2 minutes more until smooth and pourable.

Pour the filling into the cooled shell, smooth the top, and bake at 350F for 25 minutes, until the edges are set and the center still moves slightly.

Meanwhile, combine the streusel flour, brown sugar, and pecans, cut in the cold diced butter to a coarse pebbly crumb, and refrigerate until needed.

Cover the partly set filling with an even layer of streusel and bake 18 to 20 minutes more, until the topping is deep golden and the center no longer wobbles. Cool completely before unmolding and slicing.