In a stand mixer bowl, combine bread flour, granulated sugar, salt, and instant yeast.

Add warmed milk and egg, then mix on low speed until a shaggy dough forms.

Increase speed to medium and add softened butter one tablespoon at a time, kneading until the dough is smooth, elastic, and passes the windowpane test.

Place the dough in a greased bowl, cover, and let rise in a warm spot for 60 minutes or until doubled in size.

Gently degas the dough and divide into 8 equal portions (approximately 55g each).

Shape each portion into a tight, smooth ball and place on individual squares of parchment paper.

Cover and proof for another 45 to 60 minutes until the dough balls are very light and airy.

Heat vegetable oil in a heavy-bottomed pot to 170C (340F).

Carefully lower the donuts into the oil and fry for 2 to 3 minutes per side until golden brown.

Remove donuts and drain on a wire rack; allow to cool completely to room temperature.

In a chilled bowl, whip heavy cream, powdered sugar, milk powder, and vanilla extract until stiff peaks form.

Cut a deep slit vertically into the top of each donut, about three-quarters of the way through.

Pipe the whipped cream generously into the slit and smooth the surface with a spatula.

Dust the filled donuts generously with powdered sugar before serving.