Begin by making the glaze. In the top of a double boiler, mix together the egg yolks, sugar, cream, corn syrup, butter, corn starch, and salt. Continue to cook the mixture, stirring constantly, until it thickens. Remove it from the heat and stir in the maple and vanilla extracts until completely combined. Then allow to cool to room temperature before placing in the refrigerator to chill.

To make the cake, preheat the oven to 350 degrees Fahrenheit. In a medium-sized bowl, combine the flour, salt, and cocoa powder. Set aside. Cream together the butter, sugar, and eggs. Add the buttermilk to the creamed egg mixture, alternating between adding some of the buttermilk and some of the flour mixture until both are incorporated into the creamed egg mixture. Mix together the baking soda and vinegar and then add the mixture to the cake batter. Stir in the hazelnut, maple, and vanilla extracts.

Pour the cake batter into 2 well-greased and lightly floured 8-inch cake pans and bake for about 30 minutes. Remove the cakes from the oven and allow them to cool to room temperature. Drizzle the glaze and distribute the pecans between the cake layers and the top of the cake. Serve immediately.