01 - Combine flour, sugar, salt, and instant yeast in a large mixing bowl.
02 - Add warm milk, softened butter, and egg to the dry mixture. Mix thoroughly until a soft, cohesive dough forms.
03 - Knead the dough on a lightly floured surface for 8 to 10 minutes until smooth and elastic.
04 - Place dough in a greased bowl, cover with plastic wrap or a damp towel, and let rise in a warm area for 1 hour until doubled in size.
05 - Punch down risen dough and divide into 8 equal portions. Shape each piece into a smooth ball and arrange on a parchment-lined baking sheet.
06 - Cover the shaped dough and let rest for 30 minutes until slightly puffed.
07 - Heat vegetable oil in a deep pot to 340°F, monitoring with a kitchen thermometer for accuracy.
08 - Fry donuts in batches, turning occasionally, until golden brown on all sides, approximately 2 to 3 minutes per batch.
09 - Transfer fried donuts to paper towels to drain excess oil. Allow to cool completely before filling.
10 - Whip cold heavy cream to soft peaks. Add sweetened condensed milk, powdered milk, and vanilla extract. Continue whipping until stiff peaks form.
11 - Transfer cream to a piping bag fitted with a round tip. Make a small incision in the side of each cooled donut and pipe generously with filling.
12 - Roll filled donuts in powdered sugar until evenly coated. Serve immediately for optimal texture and flavor.