Mix golden flax meal and water in a small bowl until well combined. Let it rest for 5 - 10 minutes to thicken. Note: if using evaporated milk, skip this step.
In a microwave-safe bowl combine the buttermilk and butter. Microwave in 20-second increments until the mixture is warmed (110°F approx.,).
In the bowl of your stand mixer fitted with the paddle attachment, add in the flax meal mixture (or evaporated milk), buttermilk mixture, pineapple juice, vanilla, sugar, and yeast. Stir on low until combined.
Add in 2 cups of flour, potato flour, and salt and mix on medium speed for 1 minute. Gradually add in 2 1/2 remaining cups of flour until a soft dough forms.
Replace the paddle attachment with a dough hook and knead on medium speed until the dough forms a soft, smooth ball, about 10 minutes. Note: When it is ready, it will be somewhat balling around the hook and pulling away from the sides, and the dough will be super smooth and elastic and will pass the windowpane test (see note below).
Lightly spray a clean bowl with cooking spray and place the dough in the bowl. Cover with plastic wrap or a clean kitchen towel. Let rise in a warm place until puffy and doubled in size, which will take anywhere between 1 ½ to 2 ½ hours, depending on the temperature of your kitchen.
Spray a 13x9-inch baking pan with cooking spray. Set aside. Position one of the oven racks into the center of the oven. Preheat the oven to 375º F (190º C).
Gently deflate the dough and divide it into 15 equal portions (about 75 g each). Note: You can also divide the dough into 12 equal portions (94 g each) for slightly bigger rolls. Form the dough into balls and place them in the prepared pan. Cover again with the towel and allow the dough to rise for 30 minutes, or until the dough balls are puffy, and when poked gently, an indentation slowly springs back.
Mix the eggless egg wash ingredients in a small bowl.
Once the rolls have risen, lightly brush the tops of the rolls with the eggless egg wash.
Bake them for about 15 - 20 minutes or until golden brown. Brush them with melted butter immediately when they come out of the oven.
Serve warm or at room temperature.