MAKE THE CAKE: Sprinkle 2 cups of the pecans evenly over the bottoms of 3 buttered 9" round cake pans, shaking to coat both the bottoms and sides of the pans.

Combine the flour and baking soda in a bowl; mix well.

In another bowl, using an electric mixer on medium speed, cream together the butter and shortening until light and fluffy.

Gradually beat in the sugar.

Add the egg yolks, one at a time, blending well after each addition; blend in the vanilla.

Add the flour mixture and buttermilk alternately, blending well after each addition, beginning and ending with the flour mixture.

Stir in the remaining 1 cup pecans.

In a clean bowl, using an electric mixer with clean beaters on medium speed, beat the egg whites until stiff peaks form.

Fold 1/3 of the whites into the batter to lighten it; fold in remaining whites.

Pour batter evenly into the prepared pans.

Bake at 350*F.

for 25 minutes, or until a toothpick inserted in the center comes out clean.

Cool 10 minutes in pans on wire racks; invert onto waxed paper-lined wire racks.

Brush the tops and sides of the layers with the corn syrup; cool completely.

MAKE THE FILLING: Whisk together the brown sugar, corn syrup, cornstarch, egg yolks, half-and-half, and salt in a heavy 3-quart saucepan until smooth.

Bring to a boil over medium heat, whisking constantly; boil for 1 minute, or until the mixture thickens.

Remove pan from heat; whisk in the butter and vanilla.

Place a sheet of waxed paper on the surface of the mixture; chill for 4 hours.

ASSEMBLE THE CAKE: Place 1 cake layer, pecan side up, on a serving dish; spread with 1/2 the filling.

Place the second cake layer, pecan side up, over the filling; spread with the remaining filling.

Place the third cake layer, pecan side up, on top of the filling.

Serve with whipped cream; store covered in the refrigerator.

Bring to room temperature before serving.