Add the yeast, milk and sugar to the bowl of your stand mixer fitted with the dough hook attachment (or if making by hand, to a large mixing bowl). Mix with a fork and let sit for 3-5 minutes until bubbly.
Add the egg and melted butter and mix well.
Add the flour and salt and mix on low speed with the dough hook until a soft dough forms.
Continue the mixer on low speed, turning up to medium-low speed until the dough pulls away from the sides of the bowl. The dough will be soft and a little sticky - that's totally normal.
If making the dough by hand, turn it out onto a floured surface and knead for about 4-5 minutes until a soft and sticky dough forms.
Cover the bowl with plastic wrap and let rise in a warm, draft-free place for 1 hour or until the dough more than doubles in bulk.
Punch the dough down and turn it out onto a lightly floured surface. Give the dough a quick knead and form it into a large ball.
Weigh the ball of dough and divide the total weight by 20. Begin portioning out the dough according to the weight to create 20 equally-weighted pieces (mine are usually between 49 and 51 grams each). If you aren't using a kitchen scale, use a sharp knife cut the dough in half, then in half again, and then cut each of those pieces into 5 equally sized pieces.
Roll each piece into a round ball, pinching the sides down and underneath the ball of dough to create surface tension. Place on a baking sheet that's been greased and lined with parchment paper.
Preheat your oven to 375 degrees Fahrenheit and cover the pan of buns with a clean kitchen towel and let rise for about 20 minutes while the oven pre-heats.
Once the oven reaches temperature (after at least 20 minutes) brush the tops of the buns very gently with egg wash (whisk an egg with 2 tablespoons of water), sprinkle with some flaky sea salt (optional) and bake for about 20 minutes or until the buns are golden brown on top.
Let the buns cool on the pan for at least 15-20 minutes before serving.