Preheat the oven to 350 Degrees. Line a 12-muffin tin with paper muffin cups or rounds of parchment paper.
Melt the butter in a small saucepan over medium heat. Off the heat, stir in the maple syrup, ground cardamom, cinnamon, all spice, and vanilla extract. Set aside to cool.
In the mean time, mix the ground almond flour, buckwheat flour, unsweetened coconut, and baking powder in a large mixing bowl.
Add in the shredded carrot and mashed banana and mix until thoroughly incorporated. Set aside.
Using an electric mixer, beat the egg whites until softly peaking, 3-4 minutes.
Gently fold the egg whites into the flour and carrot mixture.
Pour in the butter and spice mixture. Stir until smooth.
Spoon the batter into the prepared pan, filling each cup to about three-quarters full.
Bake for 25 minutes or until golden.
In the mean time, make the frosting: Whisk together the cream cheese, honey, and lime juice in a small bowl.
Allow muffins to cool for 15 minutes on a wire rack.
When ready to eat, spoon each muffin with a tablespoon (or more) of the frosting and sprinkle it with chopped pistachios or hazelnuts.