1. Prepare the crust. In the bowl of a food processor, combine walnuts, sugar, and salt and process until nuts are finely chopped. Pour butter over mixture and pulse until combined. Press evenly over sides and bottom of a 9-inch pie pan or tart pan with a removable bottom. Freeze for 30 minutes.
2. Preheat oven to 375 degrees F. Remove crust from freezer and brush evenly with egg white. Place pan on a baking sheet and bake for 10 minutes. Crust should be browned and will puff up slightly, but will deflate as it cools. Cool completely, about 20 to 30 minutes. Increase oven temperature to 450 degrees F.
3. While crust cools, prepare the filling. In a medium saucepan, whisk yolks, whole eggs, sugar, and juice until blended. Add cornstarch, zest, and butter. Bring to a boil over medium-low heat, stirring constantly. Boil until filling thickens and is pudding-like, about 5 minutes, stirring constantly. Pour filling into cooled crust and smooth the surface.
4. Prepare the meringue. In a large bowl, combine egg whites, cream of tartar, and salt. Use an electric mixer on medium-high speed to whip until frothy. Add vanilla and half the sugar and beat until soft peaks form. Add remaining sugar gradually and keep beating until stiff peaks form. Swirl meringue on top of tart and bake until meringue is golden brown, about 3 to 5 minutes. Cool tart on a rack until it reaches room temperature, about 2 hours, then chill, if desired. Serve at room temperature or chilled.
Source: Hannaford fresh Magazine, March - April 2011