Mix the dry ingredients (3 cups flour, 3 cups sugar, 2 1/2 tsp baking powder, and 1 tsp salt) in a stand mixer with a paddle until fully combined.Mix 1 cup of room-temperature butter into the dry ingredients on a low speed. Continue to mix until no large chunks of butter remain.Pour in 1 cup of egg whites and mix on low until just incorporated, thn mix in 1 1/2 cups of buttermilk on a low speed

Add 2 tsp vanilla extract and 1/8 cup oil, and mix at a low speed until fully incorporated. Scrape down the sides of the bowl with a spatula, then beat on medium-low speed for about 30 seconds.Pour half of the batter into a separate bowl and set aside.

For chocolate cake batter Mix the additional 1/3 cup baking cocoa, 1/4 sugar, 1/4 cup buttermilk, 1/4 tsp salt, and 1/2 tsp baking powder into one bowl of vanilla batter on a low speed until combined and set aside.make the chocolate fudge swirl. Combine the chocolate chips, butter, and heavy cream into a heatproof bowl. Heat in two 30-second intervals, stirring in between. Allow the mixture to sit for 1 minute, then stir until smooth and set aside to cool.

Add chocolate and vanilla mix roughly and mix it. with a help of a stick make some design. Bake it for 30-35 min in 200° c.Allow to cool. Enjoy