Melt 2 tablespoons butter in a large skillet. Add the pecans and cook over medium heat, stirring occasionally, until toasted (about 10 minutes). Remove from heat and cool completely.

Using an electric mixer on medium speed, beat the cream cheese and 1/2 cup butter until creamy. Gradually add the sugar. Beat until light and fluffy. Stir in the buttered pecans and vanilla. Cover and chill at least 1 hour.

Place the white chocolate in a bowl and pour boiling water over it, stirring until smooth. Set aside to cool.

Using an electric mixer on medium speed, beat the butter until creamy. Gradually add the sugar, beating well. Add the egg yolks, one at a time, beating after each addition. Stir in the melted white chocolate and vanilla.

Combine the buttermilk and baking soda. Add the flour to the butter mixture, alternating with the buttermilk mixture. Begin and end with the flour. Mix at low speed after each addition just until blended.

Beat the egg whites to stiff peaks. Gently fold into the batter, making sure not to over-mix. Divide the batter evenly among the prepared pans.

Bake for 22-25 minutes, or until a toothpick inserted in the center of cake comes out clean. Cool in the pans for 10 minutes. Then, remove the cake layers from pans to wire racks to cool completely.

Spread the frosting between the layers and on the top and sides of the cooled cake. Garnish, if desired, with toasted pecans. Store in the refrigerator.