Combine pineapple juice and water in a bowl.

Add 2 tablespoons of brown sugar and all of the active dry yeast to the liquid mixture.

Stir to combine and let the yeast proof. Ensure the yeast is proofing before moving forward.

In the work bowl of your mixer, combine potato starch, masa harina, sorghum flour, rice flour, and xanthan gum.

Add salt, remaining brown sugar, and 2 tablespoons of melted butter to the dry ingredients.

Combine the ingredients until well mixed.

Add the egg and combine.

Add the yeast slurry to the mixture and combine until the dough starts to climb the paddle.

Switch to the dough hook and knead for 8-10 minutes on medium speed.

On a floured work surface, portion out the dough into approximately 5-ounce pieces.

Work in just enough flour into each piece to prevent sticking.

Shape each piece into a ball.

Place the dough balls on a baking sheet or in a baking dish and flatten them to about 1/2 the height of the ball.

Cover the buns with a moist towel and allow them to rise for at least 90 minutes.

Preheat your oven to 350°F (175°C).

Brush the tops of the buns with the remaining melted butter.

Sprinkle on your preferred toppings, such as sesame seeds.

Bake uncovered for about 50 minutes, or until the tops and bottoms are showing a nice golden-brown color and appear done.

Allow the buns to rest for 15 minutes to set their insides before slicing and serving.

Slice down the middle and serve as a sandwich or toast.