Preheat the oven to 350º Fahrenheit. Grease 2 8" round cake pans generously with shortening, then dust with flour.
Make the cake:
In a large bowl, mix together the cake mix, sugar, oil, milk, eggs and extract.
Mix for two minutes using a hand mixer or stand mixer, scraping the sides of the bowl as needed.
Fold in the black walnuts.
Pour the batter evenly between the two prepared cake pans.
Bake for 23-25 minutes or until the center of the cake springs back when you touch it.
Allow the cakes to cool for 5 minutes in the pan, then run a knife along the outside of the pans to loosen the cakes.
Turn the cakes out onto a wire rack to cool completely.
Once the cakes are cool, use a long knife to split each cake in half horizontally to make 4 layers.
Make the whipped cream:
*Homemade whipped cream works best if the cream and mixing bowl are very cold. Refrigerate the mixing bowl for at least 20 minutes before making the whipped cream.*
In the bowl of a stand mixer, beat the heavy cream, vanilla and powdered sugar until it is stiff and can hold peaks. This will take several minutes of mixing.
Assemble the cake:
Place one cake layer on a cake plate.
Top with 1/4 of the whipped cream.
Repeat with the other 4 layers. Sprinkle nuts between the layers if you'd like, or garnish the top with nuts.
Store this cake in an airtight container in the refrigerator and serve it the day you make it.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**