Follow these steps carefully for perfect Cabbage Spring Roll Cups:

1. Prepare the Cabbage Leaves: Gently remove 12-16 large outer leaves from the head of Napa or Savoy cabbage. Wash them thoroughly. Bring a large pot of salted water to a boil. Carefully place the cabbage leaves into the boiling water and blanch for 1-2 minutes, just until they become slightly tender and pliable (they should turn a brighter green). You might need to do this in batches. Immediately transfer the blanched leaves to an ice bath (a large bowl filled with ice and cold water) to stop the cooking process and preserve their vibrant color. Once cooled, carefully remove the leaves from the ice bath and pat them dry with paper towels. If the thick central stem at the base of the leaf is very rigid, you can carefully shave it down slightly with a sharp knife to make folding or cupping easier, being careful not to cut through the leaf. Set aside.
2. Prepare the Filling Base: Heat the 1 tablespoon of olive oil (or your first measure of sesame oil) in a large skillet or wok over medium-high heat. Add the ground chicken (or pork, turkey, tofu). Break it apart with a spoon and cook until browned and cooked through, about 5-7 minutes. If using tofu, cook until it’s slightly golden and firm. Drain off any excess fat if necessary.
3. Sauté Aromatics: Push the cooked protein to one side of the skillet. Add the minced garlic, grated ginger, and finely chopped onion to the empty side. Sauté for 1-2 minutes until fragrant and the onion begins to soften.
4. Combine and Cook Vegetables: Stir the aromatics into the cooked protein. Add the shredded carrots and the 4 cups of shredded green cabbage to the skillet. Cook, stirring frequently, for about 5-7 minutes, or until the cabbage has wilted significantly and the carrots are tender-crisp. You want the vegetables cooked but retaining some texture.
5. Add Optional Ingredients: If using bean sprouts and/or chopped water chestnuts, add them now. Stir them into the mixture and cook for just another 1-2 minutes – you want the bean sprouts to remain crisp.
6. Season the Filling: In a small bowl, whisk together the soy sauce (or tamari), rice vinegar, 1 tablespoon of toasted sesame oil, and optional sugar until combined. Pour this sauce mixture over the filling in the skillet. Stir everything together thoroughly to ensure the filling is evenly coated.
7. Simmer and Reduce: Continue to cook the filling for another 2-3 minutes, allowing some of the liquid to evaporate and the flavors to meld together. The filling should be moist but not overly wet. Taste and season with salt and black pepper if needed. Remove from heat.
8. Assemble the Cups: Lay a prepared cabbage leaf flat on your work surface (or hold it cupped in your hand). Spoon a generous amount of the warm spring roll filling (approximately 1/4 to 1/3 cup, depending on leaf size) into the center or base of the cabbage leaf.
9. Serve: Arrange the filled Cabbage Spring Roll Cups on a platter. Garnish generously with toasted sesame seeds, chopped cilantro, and/or sliced green onions, if desired. Serve immediately while the filling is warm, alongside your favorite dipping sauces.