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, 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 smooth ball by cupping hands and pulling dough toward you.
Place buns on a lightly greased parchment-lined baking sheet, cover, and let rise until light and puffy, about 1-1.5 hours or more depending on environment.
Preheat oven to 375°F toward the end of rising time. Make egg wash by mixing one egg with milk or cream, then brush over buns and sprinkle with coarse sea salt.
Bake for 16-18 minutes for small rolls or about 25 minutes for large rolls (100g) until golden or center roll reaches 190°F on a thermometer.
Optional: Brush with melted butter or rub a cold butter stick over the hot rolls to create a satiny, buttery crust.
