Mix sugar with milk and then add in dry yeast. Mix and leave for the yeast to activate.
Pour the rest of the ingredients into a standing mixing bowl, except for chocolate chips, butter and egg wash. Add in yeast mixture also. Mix to incorporate and then knead for 10 minutes.
Add butter bit by bit, mixing well to incorporate after each addition. Once all butter is added, knead for another 10 minutes. Place dough in a greased bowl, cover tightly with cling film and leave until the dough rises double its size.
Lightly grease your working surface. Do not use flour because we don't want to incorporate any more flour into the dough. Place the dough and lightly press into a square.
Sprinkle chocolate chips on top and lightly knead the dough to distribute well the chocolate chips. Then divide the dough into 6 equal pieces and form each piece into a ball. Place the balls in the mini panettone casings (2.5x1.75 inch or 6.35x4.4 cm), on a baking tray. This will make it easier to transfer into the oven later.
Cover loosely with a cling film and leave for the dough to rise until almost the brim. Gently brush the top surface with egg wash. Bake in a preheated oven at 350ºF (175ºC) for 25 minutes or until fully cooked. Enjoy!