Proof yeast in warm milk with a pinch of sugar for 5 minutes until foamy. If it doesn't foam, start with fresh yeast.
Mix flour, remaining sugar, and salt. Add yeast mixture, warm water, egg, and butter. Mix until a shaggy dough forms, then knead 8 to 10 minutes until smooth and elastic.
Fold in chocolate chips by flattening the dough, scattering chips across the surface, folding, and kneading gently 1 to 2 minutes.
Rise covered in an oiled bowl in a warm spot for 1 to 1.5 hours until doubled.
Divide into 9 equal pieces, shape into tight balls, and arrange in a greased pan with small gaps between each. Cover and let rise 45 to 60 minutes until puffy and touching.
Brush tops gently with egg wash. Bake at 350°F for 20 to 24 minutes until deep golden brown. Cool 10 minutes in the pan before serving.