Cut ends off plantains, peel and slice in half lengthwise. Set 2 large nonstick saute pans over medium-high heat and add oil and 2 tablespoons butter into each pan. Add plantains and cook for 10 minutes - you don't want to move it too frequently otherwise it won't caramelize as well, flipping halfway. Once you flip the plantains, sprinkle with light brown sugar (depending on the ripeness/sweetness of the plantains, adjust the sugar amount) and salt. The plantains should be nice and golden. Squeeze with fresh lime juice just before serving.