Mix together the flour, salt, sugar and yeast in a large mixing bowl (or in the bowl of an electric mixer). Pour in the egg, butter and milk, and mix on low speed until all the flour is absorbed and the dough forms a ball. If the dough seems very stiff and dry, trickle in more milk until the dough is soft and supple.
Sprinkle flour on the counter, transfer the dough to the counter, and begin kneading (or mix on medium speed with the dough hook), adding more flour, if necessary, to create a dough that is soft, supple and tacky, but not sticky. Continue kneading (or mixing) for 6 to 8 minutes. (In the electric mixer, the dough should clear the sides of the bowl, but stick every so slightly to the bottom.) Lightly oil a large bowl and transfer the dough to the bowl, rolling it to coat it with oil. Cover the bowl with plastic wrap.
Ferment at room temperature for 1½ to 2 hours, or until the dough doubles in size.
Remove the fermented dough from the bowl and divide it into twelve 3-oune pieces. Shape the pieces into tight rounds. Mist the dough lightly with spray oil and cover with a towel or plastic wrap. Allow to rest for about 20 minutes.
Line 2 sheet pans with parchment paper. Gently press down on the tops of the rolls with your fingers to flatten slightly. Transfer the buns to the sheet pans.
Mist the tops of the dough with spray oil and loosely cover with plastic wrap or a towel. Proof the dough at room temperature for 60 to 90 minutes, or until the buns have nearly doubled in size.
Preheat the oven to 400 degrees F. Brush the buns with the egg wash and garnish with poppy or sesame seeds, if desired.
Bake the buns for approximately 15 minutes, or until they are golden brown and register just about 180 degrees F in the center. The buns should cool for at least 15 minutes on a rack before serving. Store leftovers in an airtight zip-top bag. If you want to freeze them, I would wrap individually in plastic wrap and then store in a zip-top bag. Thaw at room temperature.