Stir the warm water, active dry yeast, and sugar together in a small bowl and let sit 5 minutes until frothy.
In a large bowl, whisk the 2 large eggs and melted butter until combined.
Add the gluten-free flour blend and kosher salt to the egg mixture and mix until a sticky dough forms.
Pour the proofed yeast mixture into the dough and blend until fully incorporated; the dough should remain slightly sticky—add a little more flour only if necessary.
Divide the dough into 8 equal pieces. With wet hands, shape each piece into a ball then gently flatten into bun shapes and arrange on a parchment-lined baking sheet.
Lightly cover the baking sheet with plastic wrap and let the buns rise in a warm, draft-free spot about 45 minutes, until doubled in size.
Preheat the oven to 400°F. Brush the tops of the risen buns with the beaten egg wash and sprinkle sesame seeds on top if using.
Bake the buns in the preheated oven about 20 minutes, until golden brown.
Remove the buns from the oven and cool on a wire rack 10–15 minutes before slicing and serving.