Step 1 Heat the oven to 350 degrees. Cut a lengthwise slit into each plantain and place on a parchment-lined baking sheet. Bake until the flesh is thoroughly soft and oozing through the slit, 40 to 50 minutes. Remove from the oven and set aside.
Step 2 While the plantains are roasting, make the stuffing: Finely dice the poblano chiles. In a medium bowl, combine the diced chiles, beans, green onions, cheeses and one-half teaspoon each of salt and pepper. The stuffing can be made up to a day in advance and reserved in the refrigerator.
Step 3Make the dough: Peel, trim and discard any tough ends from the plantains. In a food processor or in a stand mixer with the paddle attachment, combine the plantains and bananas with 2 teaspoons salt and puree. Be careful not to overwork the dough or it will become too starchy. Wrap the dough in plastic and chill until firm, about 2 hours.
Step 4Make the chipotle salsa: Combine the onions, chipotle chiles, tomatoes, garlic and 6 cups water in a medium saucepan. Stir in 4 teaspoons salt, 1 teaspoon pepper and the sugar. Bring to a boil over high heat, stirring occasionally, then reduce the heat and simmer, uncovered, for 20 minutes or until the liquid is reduced by about one-third and the tomato skins are falling off. Remove from the heat and set aside to cool. Pour the mixture into a blender or food processor and puree until smooth, then cover and refrigerate. This makes more salsa than is needed for this recipe. The remainder can be reserved for another use.
Step 5To assemble the empanadas, roll 2 tablespoons of the dough lightly between your palms to form a ball. Line the bottom of a tortilla press with a small plastic bag or plastic wrap and place the ball of dough in the center. Place another small plastic bag, or piece of plastic wrap, over the dough and press to form a 3 1/2 -inch circle. Place 1 teaspoon of bean stuffing on half of the circle and fold over to enclose, pressing the edges to seal. Repeat until you have used up the dough and stuffing; you should have about 30 empanadas. Place the stuffed empanadas on a tray and chill at least 30 minutes, up to a day.
Step 6Heat the peanut oil in a medium skillet over medium-high heat, until a thermometer inserted reads 350 degrees. Fry four to six empanadas at a time, shaking the pan constantly, about 1 minute until dark brown. Flip and cook the reverse side of each. Remove the empanadas and drain on paper towels.
Step 7Combine 1 cup of the chipotle salsa with the crema in a small bowl. Serve with the warm empanadas.