Preheat oven to 350°F.
Grease a bundt pan or a tube pan.
Use a hand mixer, a stand mixer or a whisk to whisk together the eggs, sugar, and oil in a large mixing bowl until pale and frothy.
Stir in the vanilla extract and the milk.
Add in the flour, baking powder and salt in the bowl with the wet ingredients.
Use a spatula or a hand mixer to combine all the ingredients.
Pour about 2/3 of the batter in the prepared pan.
Stir cocoa powder into the remaining batter in the mixing bowl.
Pour the chocolate batter over the vanilla batter in the pan.
Add the chopped walnuts.
Use a skewer or butter knife to swirl the batters together.
Bake for 40-45 minutes until a toothpick inserted in the center of the cake comes out clean.
Transfer to a wire rack and let sit for 15 minutes before unmolding the cake onto the wire rack.
Let cool completely before serving with a dusting of powdered sugar (optional).
Enjoy!