Place cashews in a bowl and cover with 1 inch of water. Soak at least 2 hours, preferrably overnight. Drain the cashews and transfer them to a high-powered blender along with the remaining ingredients. Blend until completely smooth. Transfer frosting to a sealable container and refrigerate until ready to use.
Preheat the oven to 350 degrees F and line a muffin tray with 9 muffin papers.
Mash the bananas in a mixing bowl, then mix in the eggs, pure maple syrup and vanilla extract.
In a separate bowl, stir together the remaining dry ingredients. Transfer the flour mixture to the bowl with the banana mixture and stir well until combined.
Pour muffin batter into the muffin tray, filling the holes 3/4 of the way up. Bake on the center rack of the preheated oven 18 to 25 minutes, or until muffins are golden-brown around the edges and feel firm when poked in the center.
Allow muffins to cool at least 30 minutes before frosting and serving.
*Make recipe vegan by making 2 flax "eggs." To do so, stir together 2 Tbsp ground flax seed and 6 Tbsp water in a small bowl. Allow mixture to sit, stirring occasionally, for 15 minutes, until mixture has thickened to the consistency of beaten eggs.