Step 1: In a large bowl, combine the warm milk, yeast, and 1 tablespoon of the granulated sugar. Stir gently and let sit for 5-10 minutes until foamy.
Step 2: Add the mashed bananas, melted butter, egg, remaining granulated sugar, and salt to the yeast mixture. Stir until well combined.
Step 3: Gradually add the flour, 1 cup at a time, mixing with a wooden spoon or dough hook until a shaggy dough forms. Turn the dough out onto a lightly floured surface.
Step 4: Knead the dough for 8-10 minutes, until it's smooth and elastic. It should be slightly sticky but manageable.
Step 5: Lightly grease a clean large bowl. Place the dough in the bowl, turning to coat. Cover with plastic wrap and let rise in a warm, draft-free place for 1-1.5 hours, or until doubled in size.
Step 6: While the dough rises, prepare the filling. In a small bowl, cream together the softened butter, brown sugar, and cinnamon until smooth.
Step 7: Once the dough has risen, punch it down gently. Roll it out on a lightly floured surface into a large rectangle, about 18x12 inches.
Step 8: Spread the cinnamon-sugar filling evenly over the rolled-out dough, leaving a small border around the edges.
Step 9: Starting from a long edge, tightly roll the dough into a log. Use a sharp knife or unflavored dental floss to slice the log into 12 even rolls (about 1.5 inches thick).
Step 10: Lightly grease a 9x13 inch baking dish. Arrange the sliced rolls in the prepared dish. Cover loosely with plastic wrap and let rise again for another 30-45 minutes, or until puffed up.
Step 11: Preheat your oven to 375°F (190°C). Bake the rolls for 20-25 minutes, or until golden brown on top and cooked through. If they start browning too quickly, you can loosely tent them with foil.
Step 12: While the rolls are baking, prepare the cream cheese frosting. In a medium bowl, beat the softened cream cheese and butter until light and fluffy.
Step 13: Gradually add the powdered sugar, mixing until smooth. Beat in the vanilla extract, then add milk or heavy cream 1 tablespoon at a time until the desired consistency is reached (creamy but spreadable).
Step 14: Once the rolls are out of the oven, let them cool for about 5-10 minutes, then generously spread the cream cheese frosting over the warm rolls. Serve immediately and enjoy!