These grown-up lemon bars are made with paper-thin slices of lemon, giving the sweet filling a pleasant bitterness.
In a bowl, using an electric mixer, beat the 1 stick plus 2 tablespoons of butter with the sugar and egg yolk until smooth. Add the flour, baking powder and salt and beat at low speed until evenly moistened, about 2 minutes. Using your hands, knead once or twice to bring the dough together.
Using a mandoline or very sharp knife, slice the lemon halves as thinly as possible and transfer to a medium bowl; pick out the seeds. Stir in the lemon juice and sugar. Cover with plastic wrap and refrigerate overnight.
Butter a 9-inch square metal baking pan. Pat three-fourths of the dough into the baking pan in an even layer. Roll the remaining dough into eight 9-inch-long ropes. Transfer to a plate. Refrigerate the crust and ropes until firm, about 10 minutes.
Using an electric mixer, beat the flour, butter and eggs until smooth. Fold in the lemon-sugar mixture.
Preheat the oven to 350°. Spread the filling over the dough and arrange the ropes of dough on top in a crisscross pattern. Bake in the lower third of the oven for 40 to 45 minutes, or until the ropes are golden. Let cool completely.
Run the tip of a knife around the edge of the pan. Cut the square into 18 bars and serve.
very different cookie bar. textured from the whole lemon slices, just sweet enough. lattice ropes are attractive, more like a shallow pie than a bar cookie