Preheat oven to 350 degrees F. Lightly grease an 8x8-inch square baking pan.
In a small bowl place 1 cup of cake mix, nuts, and 1/2 teaspoon cinnamon. Mix to combine. With two knives gently cut in 1/4 cup cold butter until crumb forms. Set aside.
Place remaining cake mix in large bowl. Add 1/3 cup melted butter, 2/3 cup eggnog, eggs, and 1 teaspoon cinnamon. Mix until just combined. Pour cake mix into prepared pan.
Sprinkle crumb mixture on top of cake batter. Bake cake about 30-35 minutes or until golden brown around edges. Cool completely.
Meanwhile, in a small bowl whisk together 1 cup frosting and remaining 1/2 cup of eggnog. Drizzle over top of cooled cake.
SNAPPY TIPS: Cool cake completely before drizzling frosting on top.SNAPPY SUBSTITUTIONS: Instead of cinnamon, you could use your favorite spice such as Pumpkin or Apple Pie spice. Instead of eggnog you could use milk.