Preheat the oven to 320°F (160°C) using static heat (no fan).

In a large mixing bowl, whisk together the egg yolks and canola oil until just combined. Add ½ cup (100 grams) of the sugar and whisk until smooth. Alternate adding half the flour and half the milk or orange juice, whisking to combine after each addition. Add the remaining flour, baking powder, and remaining liquid, whisking again until smooth and lump-free.

In a stand mixer fitted with the whisk attachment, beat the egg whites on medium speed until foamy. Gradually add the remaining 1 cup (200 grams) sugar and whip on high speed until stiff, glossy peaks form. Gently fold one-third of the whipped egg whites into the yolk batter to lighten it, then carefully fold in the next third. Add the final third and fold with a balloon whisk to fully incorporate, ensuring no streaks remain.

Transfer one-third of the finished batter to a separate bowl. Sift in the cocoa powder and whisk gently until smooth.

Pour the plain batter into an ungreased 10-inch (26 cm) Bundt pan. Smooth the surface. Carefully spoon the cocoa batter on top. Using a knife, swirl the batters together to create a marbled pattern, ensuring the cocoa doesn't sink to the bottom. Bake for 1 hour and 10 minutes. Do not open the oven during baking.

Remove from the oven and immediately invert the pan if using an angel food-style Bundt pan with legs. Let the cake cool upside down for at least 3 hours or overnight.

Once fully cooled, carefully release the cake with a small offset spatula. Transfer to a serving plate and dust with powdered sugar.