Melt butter in skillet over medium heat. Slice in bananas and cook gently until the bananas break up and become mushy and fragrant. Stir in cinnamon, nutmeg, and salt for a minute. Remove bananas from heat and cool to room temperature.
In a bowl or pitcher, blend bananas with cream or cultured cream until very smooth. (You can use either a mixer or a blender for this.)
Add honey, milk or kefir, vanilla, and egg yolks if using. Blend until smooth.
Process in ice cream maker as the manufacturer directs.
Stir in walnuts (if using) and freeze ice cream in a covered container until ready to serve.
If you don't serve the ice cream within the first couple of hours, you may need to soften it at room temperature before scooping. (If you used the egg yolks, it will be softer.)