Instructions: Make applesauce filling:
Quarter and core apples (do not peel). In a 5-quart saucepan simmer apples, uncovered, with remaining filling ingredients 2 hours, or until mixture is reduced to about 3 3/4 cups. (Stir mixture frequently during last 30 minutes of cooking to prevent scorching.) Force mixture through a food mill fitted with coarse disk or a medium-mesh sieve into a bowl, discarding solids, and chill. Applesauce may be made up to 3 days ahead and chilled, covered.

Preheat oven to 375F.

Make cookie crust:
In a food processor grind hazelnuts fine with sugar, flour, and salt. Add butter and pulse mixture well. Add yolk mixture, 1 tablespoon at a time, pulsing after each addition, and pulse mixture until it forms a dough.

Press dough onto bottom and up side of a 10-inch tart pan with a removable fluted rim. Bake crust in middle of oven 25 minutes, or until browned lightly, and cool in pan on a rack. Crust may be made 3 days ahead and kept, covered, in a cool dry place.

Spread applesauce onto crust.

Preheat oven to 450F.

Make meringue:
In a bowl with an electric mixer beat egg whites with a pinch salt until they hold soft peaks. Add sugar gradually, beating whites until they hold stiff peaks.

Transfer meringue to a pastry bag fitted with a 1/2-inch star tip and pipe some in a lattice pattern over filling. Pipe remaining meringue onto edge of tart to make a decorative border.

Bake tart in middle of oven 10 minutes, or until meringue is golden, and chill 30 minutes or up to 3 hours.

To toast and skin hazelnuts:
Preheat oven to 350F.

In a baking pan toast hazelnuts in one layer in oven 10 to 15 minutes, or until colored lightly, and skins blister. Wrap nuts in a kitchen towel and let steam 1 minute. Rub nuts in towel to remove as much of skins as possible and cool.

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