Add the vegetable oil to a large pot.
¼ cup vegetable oil
Line the bottom of the pot with the reserved cabbage leaves.
To make your cabbage rolls, take a cabbage leaf and cut away any remaining hard part (usually found in the middle of the leaf and going up about an inch or two). You can decide at this point to cut your cabbage leaf in half (to make small cabbage rolls) or leave it whole (to make larger cabbage rolls). We think the latter is easier.
Place some filling in the bottom-center of your leaf (where the core would have been). The amount of filling you use will depend upon whether you use an entire or half a cabbage leaf, and on the size of your leaf. Use your judgment. We used about 2 tablespoons of filling for an entire cabbage leaf.
Use the cabbage leaf to fold over the filling. Bring in the sides, and continue to roll up. It is almost like you are making a burrito. The key is to make sure that the filling is snug within the cabbage leaf so that it does not fall out. Because the rice will increase in volume as it cooks, do not wrap your cabbage rolls too tightly. Watch video here. As you fold each one, place them seam side down in the sauce pot.
Repeat until all of the filling, or all of the cabbage leaves, are used.
When you have placed all of your cabbage rolls in the pot, you can layer the top with any remaining cabbage leaves. Sprinkle with salt and pepper.
Boil some water in a kettle. Pour about 2 cups of boiling water into the pot with the cabbage leaves, along with the crushed tomato sauce or passata.
2 cups boiling water, 1 cup crushed tomato sauce of passata
When the water and tomato sauce come to a boil, reduce heat to medium. Cook, covered for about 1 hour 10 minutes. You can always remove a cabbage roll at this point to taste it and make sure that the rice is cooked. Remove any top layers of cabbage that you had covering your cabbage rolls and set aside.
Let cool a bit, serve and enjoy!