These bars were inspired by a recipe from Maida Heatter.
Crust: Preheat oven to 350 degrees. Butter a 9-by-13-inch baking dish and line with parchment, leaving a 2-inch overhang on long sides. Butter parchment. Whisk together flour, confectioners' sugar, and salt in a bowl. Work in butter with your fingertips until combined and mixture holds together when pinched. Press crust evenly into bottom of prepared pan. Freeze 15 minutes. Bake crust until light golden brown, 20 to 25 minutes.
Filling: Meanwhile, in a heatproof bowl, soak dates in boiling water 15 minutes. Drain, reserving liquid. Puree dates in a food processor with enough of soaking liquid (about 1/2 cup) to make a spreadable paste. (You should have about 1 1/4 cups.)
While dates are soaking, whisk together granulated sugar, flour, and salt in a bowl. Whisk in eggs, then lemon zest and juice.
Spread date paste evenly over baked crust. Bake 4 minutes. Reduce heat to 325 degrees, pour filling over date layer, then bake until just set, about 20 minutes more.
Let cool on a wire rack 20 minutes. Run a paring knife around edges, then lift out of dish using parchment. Let cool completely. Dust with confectioners' sugar. Cut into squares.