In a bowl, combine warm milk, sugar, and yeast. Let it sit for 5–10 minutes until foamy.
Add flour, egg, melted butter, and salt. Mix until a soft dough forms.
Knead the dough for 8–10 minutes until smooth and elastic.
Place the dough in a greased bowl, cover, and let it rise for 1–2 hours until doubled in size.
Roll the dough out on a lightly floured surface to about 1 cm thickness.
Cut the dough into donut shapes using a donut cutter.
Place the donuts on a tray, cover, and let them rest for 30–45 minutes.
Heat oil in a deep pan and fry the donuts until golden brown on both sides.
In a bowl, mix granulated sugar and ground cinnamon.
Coat the warm donuts generously with the cinnamon-sugar mixture and serve.