In a small, heavy-bottomed saucepan, melt the butter or ghee over medium heat.
Add the mustard seeds and cook, stirring, until they begin to pop and become fragrant, about 1-2 minutes.
Stir in the cayenne pepper and cook for another 30 seconds until aromatic.
Add the flaked coconut and stir constantly until it's lightly toasted.
Add the mashed bananas, stir to combine, and immediately remove from the heat.
In a separate medium bowl, whisk together the yogurt, salt, and sugar until smooth.
Scrape the warm banana and spice mixture into the yogurt and stir gently to combine.
Cover and chill in the refrigerator for at least 2 hours before serving to allow the flavors to meld.
