Combine all dough ingredients except butter in a stand mixer bowl. Mix on low speed for 1-2 minutes until flour is absorbed, then mix on high or medium-high speed for about 10 minutes until soft and smooth.
Add softened butter and mix for a few more minutes until fully combined. Shape dough into a ball, cover, and let rise until nearly doubled in size, about 1-2 hours.
Gently deflate dough and divide into 15-24 rolls depending on desired size (105g for extra large, 63g for standard). Shape each piece into a ball by cupping hands and pulling dough toward you to create a smooth, tight outer layer.
Place buns on a lightly greased parchment-lined baking sheet, cover, and let rise until light and puffy, about 1-1.5 hours. Preheat oven to 375°F toward the end of rising time.
Make egg wash by mixing one egg with milk or cream. Brush over buns and sprinkle with coarse sea salt.
Bake small rolls for 16-18 minutes until golden, or large rolls for about 25 minutes until internal temperature reaches 190°F. For XL rolls, remove when center roll reaches 185°F.
Once out of the oven, brush with melted butter or rub a cold butter stick over the top to melt and create a satiny, buttery crust.
