I personally LOVE a good mash banana face mask, especially in the winters when my skin gets super dry and itchy. Bananas are loaded with vitamins and minerals like potassium which are super good for your skin.
I usually mash half a ripe banana and either mix in a little bit of plain Greek yogurt OR honey to give it that spreadable consistency. Apply it to clean skin and leave it on for a good half hour - I find the longer I leave it on, the smoother and more hydrated my skin in.
If you find the consistency to be too thick or unspreadable, you can always add a little bit of water or milk (milk is also hydrating and helps get rid of dead skin cells). You can also run it through a blender or food processor as well!