Preheat oven to 350 degrees F (175 degrees C). Grease two 8-inch round cake pans.
Beat egg whites in mixing bowl until medium-stiff peaks form; set aside. Sift together flour and cocoa powder; whisk in ground pecans and set aside.
In a separate bowl, beat egg yolks; mix in 2/3 cup sugar, vanilla, and 1/2 teaspoon instant coffee granules and beat well. Fold yolk mixture into egg whites. Gently fold in flour, cocoa, and pecan mixture. Spread batter into prepared pans.
Bake in preheated oven until cake springs back when lightly touched with a finger and a tester inserted in the center comes out clean, about 25 minutes. Let cakes cool slightly, then remove from pans to cool completely on wire racks.
To Make Mocha Cream: Dissolve 1 tablespoon coffee granules in boiling water. Cool. Beat whipping cream and 2 tablespoons of sugar together in a cold mixing bowl until stiff. Mix in cooled coffee.
Fill and frost cake with Mocha Cream and garnish with pecan halves. Keep refrigerated until ready to serve.