Melt the butter with the olive oil in a saucepan over medium-high heat. Add the serrano chile and cook until the chile begins to brown, about 1 minute. Add the beans and chicken broth. Cook over medium heat, frequently mashing only the beans (not the chile), until the beans are a thick paste, about 10 minutes. Season with salt and pepper. Remove the chile and serve.
Recipe courtesy of Marcela Valladolid