Melt the butter and set aside. In another bowl, beat the egg lightly.
In a large mixing bowl, sift the flour and add salt, yeast, castor sugar, and milk powder (if using). Add the beaten egg, lukewarm water, milk, and melted butter.
Knead the Dough:
Mix until a soft dough forms. Knead for 10 minutes until smooth and elastic.
Let It Rise:
Lightly oil a clean bowl, place the dough inside, and coat the top with a thin layer of oil to prevent drying. Cover with plastic wrap and let rise in a warm place (like your oven with the light on) for 1–3 hours, until doubled in size.
Shape the Doughnuts:
Punch down the dough and knead for 1 minute. Divide into 8 equal pieces, shape into rounds or ovals, and place on a floured surface. Cover with a clean cloth and rest for 30 minutes.
Fry the Doughnuts:
Heat oil in a deep pan over medium-high heat. Fry the doughnuts until golden brown on both sides. Remove and drain on paper towels. While still warm, roll them in castor sugar to coat.
Prepare the Fresh Cream Filling
