Trim the dark green tops from the leeks. Cut the leeks in half lengthwise, then slice into thin half-moons. Rinse thoroughly in a colander under running water to remove any dirt.
In a large skillet over medium heat, melt the butter with the olive oil. Add the minced garlic and sauté until fragrant, about 1 minute.
Add the prepared leeks to the skillet. Season with salt and pepper. Cook, stirring occasionally, until the leeks are tender and slightly caramelized, about 10-15 minutes. Serve as a side dish.
