Ingredients
Equipment
Method
- Preheat the oven. Preheat to 350°F / 175°C. Position a rack near the center.
- Prepare the pans. Grease and flour either one deep 10 x 16-inch / 25 x 41-cm pan or three 9 x 5-inch / 23 x 13-cm loaf pans. For loaf pans, parchment along the bottom and long sides makes removal easier.
- Combine the eggs and sugars. Place the 12 eggs, 4 cups / 800 g sugar, and 3 Tbsp / about 36 g vanilla sugar in the bowl of a large mixer.
- Beat for the full 15 minutes. Beat on high for about 15 minutes, until very pale, thick, foamy, and dramatically increased in volume.
- Check the ribbon stage. Lift the whisk. The mixture should fall back in a thick ribbon that remains visible for a few seconds. If it still looks thin and watery, keep beating.
- Combine flour and baking powder. Whisk together the 6 cups / 720 g flour and 2 Tbsp / 24 g baking powder for about 30 seconds.
- Lower the mixer speed. Turn the mixer to low. From this point forward, mix gently so you do not knock out the air created during whipping.
- Add the oil slowly. Pour in the 2 1/2 cups / 600 mL oil in a slow, steady stream. Mix only until incorporated.
- Add the water slowly. Add the 1 1/2 cups / 360 mL water gradually, keeping the mixer on low.
- Add the flour mixture. Add in about 3 additions. Mix on the lowest speed only until smooth and no dry streaks remain.
- Reserve the chocolate portion. Measure 2 1/2 cups / 600 mL batter into a separate bowl.
- Fill the pans. Pour the remaining vanilla batter into the prepared large pan or divide it evenly among the three loaf pans.
- Make the chocolate batter. Add the cocoa powder and 5 Tbsp / about 63 g sugar to the reserved batter. Stir or fold gently until evenly incorporated.
- Add the chocolate batter. Pour or spoon it across the vanilla batter in broad lines or dollops. If using three loaf pans, divide it reasonably evenly among them.
- Marble the cake. Run a butter knife or fork through the batter using broad S-shaped or figure-eight strokes. Stop after about 6-8 passes. Do not mix until the batter turns brown.
- Bake the large cake. For one deep 10 x 16-inch pan, begin checking around 60 minutes. Expect about 60-75 minutes total.
- Bake the loaf cakes. For three loaf pans, begin checking around 55 minutes. Expect about 55-70 minutes total.
- Check for doneness. The top should be golden, the center should spring back lightly, and a long skewer inserted into a vanilla area should come out clean or with a few moist crumbs.
- Optional thermometer check. About 205°F / 96°C in the center is a useful secondary check. Use it together with the visual cues.
- Cool. Let loaf cakes cool in their pans 15-20 minutes before removing. A large 10 x 16 cake may cool completely in its pan. Allow about 1 hour before slicing.
Notes
Pan Size
This makes a lot of batter. Use one deep 10 x 16-inch / 25 x 41-cm pan, preferably about 2 1/2 inches / 6 cm deep, or three 9 x 5-inch / 23 x 13-cm loaf pans. Do not fill any pan more than about two-thirds to three-quarters full. If your large pan is shallow, use the loaf-pan option.
Make Ahead, Storage & Freezing
- Make ahead: Bake 1-2 days before serving, cool completely, and wrap airtight.
- Room temperature: Up to 3 days.
- Refrigerator: Up to about 5 days; bring toward room temperature before serving.
- Freezer: Wrap tightly and freeze for up to 3 months.
