In a microwave-safe bowl, warm milk, pineapple juice, and vanilla extract for about 15 seconds until just warm.
In a standing mixer bowl, whisk together brown sugar, instant yeast, gluten-free flour, tapioca starch, and xanthan gum.
Add egg, egg yolk, and the warmed milk mixture to the dry ingredients in the mixer bowl. Mix until smooth.
Incorporate softened unsalted butter and salt into the dough, continuing to mix until smooth.
Transfer the dough to a lightly floured surface and knead for 10 minutes.
Shape the dough into a ball and place it in an oiled bowl. Cover with a warm towel and let it rest for 45 minutes or until it doubles in size.
Lightly grease a 9x13-inch baking pan and set it aside.
Divide the dough into 12 equal portions and shape them into balls. Arrange the balls in the prepared pan, cover them with a towel, and let them rest for another 45 minutes.