You can speed up the process ASAP by tossing the bananas, peel and all, onto a baking sheet and baking in a 300 degree oven for about 10 minutes.  Remove from the oven once they start to look brown and shiny, and let them cool completely before mashing and using in this recipe. 2. If you aren’t planning on making this recipe for a few days, you can toss unripe bananas into a paper bag for 1-3 days to accelerate the process.