FILLING:

2 thin-skinned lemons, sliced thin and seeded
5 lg. eggs
1 c. sugar

CRUST:

1 1/2 c. lightly toasted and cooled walnuts, ground
1 1/4 c. all-purpose flour
1/4 c. sugar
1 stick (1/2 c.) unsalted butter, softened
2 tbsp. lightly beaten egg

TOPPING:

1/4 c. all-purpose flour
1 c. sugar
1 stick (1/2 c.) cold unsalted butter, cut into bits

Whipped cream

Make the filling. In a food processor puree the lemon slices and with the motor running add the eggs, 1 at a time and the sugar. Transfer the filling to a bowl and chill it, covered, for at least 8 hours or overnight.

Make the crust. In a food processor blend together the walnuts, the flour, and the sugar and add the butter and the egg, pulsing until the mixture just forms a dough. Press the dough onto the bottom and up the side of a 9 inch tart pan with a removable fluted rim and chill it for at least 1 hour or overnight.

Make the topping. In a small bowl blend together the flour, the sugar and the butter until the mixture resembles coarse meal.

Pour the filling onto the crust, sprinkle the filling with the topping, and bake the tart in the middle of a preheated 350 degree oven for 40 to 45 minutes, or until the topping is golden. Serve tart warm with the whipped cream.