Swiss Chard W/ Pancetta

This recipe works with any greens, I like chard so much, and it grows here practically year round!
2 tablespoons extra-virgin olive oil
2 ounces pancetta, finely diced (bacon or 1/4 cup of pine nuts or walnuts work as well)
2 garlic cloves, thinly sliced
1/2 teaspoon chopped rosemary
1 1/2 pounds Swiss chard or rainbow chard, stems and inner ribs cut into 1/2-inch pieces, leaves cut into 1-inch ribbons
Salt and freshly ground pepper
1 1/2 teaspoons red wine vinegar

Heat the oil in a large, deep skillet. Add the pancetta, garlic and rosemary and cook over moderately high heat until the garlic is softened, about 2 minutes. Add the chard stems and cook, stirring occasionally, until crisp-tender and lightly browned, about 7 minutes. Add the chard leaves, season with salt and pepper and cook, tossing, until wilted, about 5 minutes. Stir in the vinegar, toss to coat and serve.