To make the crust, mix together the flour, sugar, and salt in a standing mixer, using the paddle attachment to combine. Add the butter and mix on low speed until the dough is just uniformly moistened, but not yet gathered into a single mass. Pour the crumbles into an 8 x 8 baking pan and use your palms to flatten it into a level layer. Bake for 20 to 25 minutes, until faintly golden. Cool on a wire rack and reduce the oven temperature to 325°.
To make the filling, beat the eggs until foamy, about a minute. Add remaining ingredients and beat until thoroughly combined. Pour the filling over the crust and carefully transfer to the oven. Bake for 25 to 30 minutes, turning the pan halfway through, until the center is just set. Cool completely.
To serve, cut into to squares and then dust lightly with confectioners sugar.