Fill a Dutch oven or cast iron pot with a few inches of peanut or canola oil and heat on medium-high until it reaches 375°F.

In a large bowl, stir together the bananas, flour, cornstarch, coconut, sugar, baking powder, and salt, followed by the egg yolks, milk, and vanilla. Combine the mixture using a potato masher until it becomes a thick yet viscous batter, adding more milk — tablespoon by tablespoon — if necessary.

Using a springform ice cream scoop to form the fritters, carefully lower 4 to 5 dollops of batter into the hot fry oil at a time (I gently slip the scoop into the oil, then release the batter by squeezing the clamp a few times). Cook, flipping once, until the fritters are a nice golden-brown, approximately 2 to 3 minutes. Remove the fritters with a slotted spoon or spider, shaking off excess oil back into the pot, and place on a paper towel-lined sheet pan to cool.

Continue with the remaining batches, making sure to return the oil to 375°F in between batches. Let fritters cool for 5 to 10 minutes. Sprinkle generously with powdered sugar and serve warm.