Swiss chard has only recently become a popular vegetable in America, but I grew up on it and loved it. This was my favorite way of cooking it. Chard can be found with beautifully colored stems, which really adds to the presentation of this dish. Traditionally we used regular potatoes, but now I sometimes replace them with sweet potatoes. This dish is especially good when made in advance and reheated.
Trim the ends from the stems of the chard leaves. Cut off and discard any wilted or yellow parts of the leaves. Strip the stems from the leaves, and cut the stems into 1/2-inch lengths. Cut the leaves in half lengthwise, then crosswise into 1/2-inch strips. Wash the leaf and stem pieces thoroughly; then drain them well.
Bring 4 quarts water to a boil in a large pot. Add the potatoes, and cook until almost tender, about 15 minutes. Add the Swiss chard, and cook until the vegetables are tender, an additional 10-15 minutes. Drain well.
Heat 2 tablespoons of the olive oil in a large skillet over medium heat. Add the garlic and cook just until it begins to turn golden, about 1 minute. Add the Swiss chard and potatoes, and season them lightly with salt and pepper. Cook, stirring and smashing the potatoes, until the liquid is evaporated and the potatoes are coarsely mashed. If the potatoes begin to brown, adjust the level of heat to medium low and continue stirring. Add the remaining 2 tablespoons olive oil, season to taste with salt and pepper, stir, remove garlic and serve hot.