You could use regular cabbage here–just add it a couple of minutes before the radicchio and let it soften a bit, then add the radicchio and continue with the recipe.
1 T olive oil, or use all butter
2 T butter, or use all oil
1 c diced onion, or thinly sliced leeks, white and pale greens parts
3 garlic cloves, minced
1/2 head Napa cabbage, thinly sliced
1 head radicchio, thinly sliced
1 c vegetable or chicken broth, or water
2 T red wine vinegar
salt and pepper, to taste
1. Heat the oil and butter in a large skillet or saucepan over medium heat. Add the onion or leeks and cook, stirring, until softened (leeks will soften sooner than onions). Add the garlic and cook another minute or so. Add the cabbage and radicchio, increase the heat to medium-high and cook, stirring occasionally, until the cabbage is wilted and starting to brown, about 3 to 5 minutes.
2. Add the broth and cook until the vegetables are tender and the broth has evaporated. Stir in the vinegar and cook until the vinegar has evaporated. Season with salt and pepper and serve.