In a mixing bowl, combine warm milk and yeast. Let it sit for 5 minutes until frothy.

In another bowl, whisk together flour, sugar, and salt. Add the yeast mixture, eggs, and melted butter. Mix until a dough forms.

Knead the dough on a floured surface for about 10 minutes until smooth. Place in a greased bowl, cover, and let rise for 1 hour or until doubled in size.

Once risen, punch down the dough and roll it out to about 1/2 inch thick. Cut out circles using a cookie cutter.

Let the circles rise for another 30 minutes. Heat oil in a frying pan to 350°F (175°C).

Fry the donuts in batches until golden brown, about 2-3 minutes per side. Remove and drain on paper towels.

Fill a pastry bag with pastry cream or jam. Poke a hole in each donut and fill with the desired filling.

Mix sugar and cinnamon in a bowl. Roll each filled donut in the mixture to coat.