Prep: Grease or spray a 9×13 inch baking dish with vegan butter or oil and set aside. It’s important to ensure that the butter is softened for both the dough and filling before starting the recipe to achieve a smooth consistency.
Mash the Banana: Peel the bananas and break them into chunks in a medium bowl. Use a fork to mash the bananas, then give the mixture a vigorous stir to break up the fibers even more; the finished mash should look glossy. Measure out 3/4 cup of mashed banana and save the remainder for smoothies.
Warm the Milk: In a small pot on the stovetop, warm the soy milk and vanilla until it reaches between 110 to 115F (just when the milk starts to steam). Alternatively, you can combine the soy milk and vanilla in a small bowl and microwave for 45 seconds. Set aside.
Dry Ingredients: In the bowl of a standing mixer with a dough hook attachment, whisk together the flour, granulated sugar, cinnamon, and active yeast. Sprinkle the kosher salt on top.
Wet Ingredients: Add the mashed banana and warmed soy milk to the bowl. Mix until a shaggy dough forms.
Knead: Knead the dough on medium-low speed for 8 to 10 minutes in total. Once all of the flour has been incorporated with the wet ingredients, begin to add the vegan butter 1 tablespoon at a time. Wait until the butter has been fully incorporated into the dough (about 1 minute) before adding the next tablespoon. The dough should look and feel smooth when ready.
Roll: Dust your work surface and a rolling pin with flour, then transfer the dough to the work surface. Roll it out until it forms a 12×20 inch (30×50 cm) rectangle.
Fill: In a small bowl, mix the dark brown sugar and 1 tablespoon of cinnamon together, then set aside. Use a spatula or offset spatula to spread the remaining vegan butter over the dough, leaving a 1/2 inch border on one long side. Sprinkle the sugar mixture evenly over the butter, gently pressing into the butter so it sticks. Top the sugar mixture with the sliced bananas and walnuts if using.
Roll: Starting with the long edge that has no free border, roll the dough toward the long edge with the bare border. Pinch the dough ends together to seal the cinnamon roll better.
Slice: Slice the rolls into 12 even pieces using a long string of dental floss; slide the floss under the roll, then “cross” the two free ends over the top and pull down to create a clean slice. Alternatively, you can use a sharp knife, but they won’t look as neat.
Rise: Transfer the rolls into the prepared baking sheet. Cover with plastic wrap and let rise in a warm place for 1 hour, until the rolls have almost doubled in size.
Overnight Option: You can immediately transfer the covered rolls to the fridge and store chilled for 10 to 12 hours. Let the rolls come to room temperature on the counter for 30 minutes before baking.
Preheat: While the rolls rise, preheat the oven to 350F. It’s a great time to remove the frosting ingredients from the fridge so they have time to soften.
Bake: Bake in the oven for 25 to 30 minutes, until the rolls have risen and are lightly golden brown. For crispier rolls, bake for 30 to 35 minutes. Set the baking dish on a cooling rack to let the rolls cool while you prepare the icing.
Icing: In a medium bowl, add the softened vegan butter, cream cheese, powdered sugar, and vanilla. Use a stand mixer or hand mixer to beat the icing until it’s smooth and fluffy, scraping the sides of the bowl as necessary.
Serve: Use a spoon to dollop frosting on top of each cinnamon roll while they are still warm, then use a spatula to spread the frosting into each nook and cranny of the rolls. Serve warm for the best experience.
Storage: Let the cinnamon rolls cool completely before storing in the refrigerator, where they will keep in an airtight container for up to 3 days. You can also freeze leftover cinnamon rolls for up to 2 months.