In the bowl of a stand mixer, add the yeast (6g), the cooled milk (170g), and a pinch of the sugar. If using active (not instant) yeast, let sit until foamy (8-10 minutes?). If using instant (not active) yeast, proceed.
Add the melted butter (15g), sugar (15g), and the egg.
In a small bowl mix together the bread flour (300g) and salt (6g).
With the dough hook attached and the mixer on low, add the flour mixture to the milk/egg/yeast/sugar mixture until all added and a dough forms. Mix on medium-low (3 or 4) for 5-8 minutes.
Transfer the dough to a lightly oiled bowl, cover, and let rest until doubled in size, 60-90 minutes, depending on temperature. (It took almost 2 hours for me in winter with my house at ~65℉.)