In the bowl of a stand mixer, combine yeast and 1 teaspoon sugar. Add warm water, mix by hand, and set aside until the yeast blooms/foams (about 5 minutes).
Add remaining sugar, 2 cups of flour, butter, milk, egg, and salt. Using the dough hook attachment on your stand mixer, mix on low speed until the ingredients are fully combined (3-5 minutes).
Add remaining flour, ¼ cup at a time, mixing on low to get most of the flour incorporated after each addition until the dough pulls away from the sides of the bowl. (If the dough is not pulling away from the sides of the bowl, add a little more flour.)
Knead with the dough hook for 5-6 more minutes, or until smooth.
Transfer to a greased bowl, cover with greased plastic wrap, and let rise until doubled (about 1 hour).
Line a baking sheet with parchment paper.
When ready, punch down the dough and turn it onto a lightly floured surface.
Divide the dough into two equal portions (about 515g each), and roll each into a circle about 12 inches wide and ¼-inch thick.
Use a pizza cutter to slice each dough circle into 12 equal wedges (24 total wedges).
Starting on the wide edge of each wedge, roll towards the tip. Place tip side down onto the lined baking sheet about 2 inches apart.
Pull the edges slightly together to create the curved crescent shape.
Loosely cover the rolls. Let them rise until doubled in size (about 30 minutes).
Preheat the oven to 350°F.
Bake the rolls for 12-14 minutes, or until golden brown.
Brush with melted butter and sprinkle with kosher salt. Serve warm or cold!