Whisk the warm milk, sugar, and active dry yeast in a bowl. Wait 5 minutes until frothy.
Add the gluten free all-purpose flour, softened butter, 2 of the eggs, and salt to the yeast mixture. Beat on medium speed for 3 minutes until a smooth, slightly sticky dough forms.
Divide the dough into 6 equal portions. With wet hands, shape each portion into a smooth, round bun and place on a parchment-lined baking sheet.
Lightly press the tops to flatten them slightly. Cover with a damp towel and let rise for 40 minutes.
Preheat the oven to 375F. In a small bowl, beat the remaining egg and gently brush it over the top of each risen bun.
Sprinkle the sesame seeds evenly over the egg-washed buns.
Bake for 18 to 22 minutes until deeply golden brown and shiny. Allow to cool completely on a wire rack before slicing.