CRUST:

Rind (colored part only) of 1 lemon, removed with a zester or grater
1 c. unbleached all-purpose flour
2/3 c. firmly packed light brown sugar
6 tbsp. unsalted butter, chilled, cut in thirds
1/4 c. toasted walnuts (see cook's notes)
Pinch of salt

FILLING:

Rind (colored part only) of 1 lemon, removed with a zester or grater
3/4 c. granulated sugar
2 lg. eggs
1/3 c. fresh lemon juice
1 tsp. unbleached all-purpose flour
1/4 tsp. baking soda
3 tbsp. coarsely chopped toasted walnuts (see cook's notes)
1 tsp. confectioners sugar

COOK'S NOTES: To toast walnuts, spread in a single layer on a baking sheet. Bake in a 350°F oven until light brown and fragrant, 8 to 10 minutes, watching carefully so they do not burn.

PRELIMINARIES: Fifteen minutes before baking, place rack in center of oven and preheat to 350°F. Have a 9-inch square baking pan ready.

PROCEDURE FOR CRUST: In food processor fitted with metal blade, combine lemon rind, flour, sugar, butter, walnuts and salt. Pulse the processor until both the butter and walnuts are the size of small peas. (Mixture will be very crumbly.) Distribute crumbs over bottom of baking pan and press into place with your fingers. Bake in a 350°F oven until the crust is lightly browned, about 25 minutes.

PROCEDURE FOR FILLING: In bowl, whisk lemon rind, sugar and eggs until fluffy. Add the lemon juice, flour and baking soda and mix until smooth. Pour over the crust. Return to oven and continue baking until filling is just barely set and very lightly colored, 12 to 15 minutes. Remove from the oven and sprinkle walnuts over the top.

PRESENTATION: Cool completely before cutting in squares. Store in an airtight container for up to 2 days, if desired. Just before serving, sift confectioners sugar over the top.

YIELD: Makes 16 (2-inch) squares.