Prepare the Dough:

In a large bowl, mix flour, sugar, salt, and yeast.

In a saucepan, warm milk and butter until melted. Cool slightly.

Add milk mixture and egg to the dry ingredients. Knead into a smooth dough.

Let dough rise in a warm place, covered, for about 1 hour until doubled.

Shape the Donuts:

Roll out the dough on a floured surface to 1/2-inch thickness.

Cut into donut shapes using a pastry cutter.

Let cut donuts rise for 30 minutes.

Make the Filling:

Whip heavy cream with powdered sugar and vanilla until stiff peaks form.

Gently fold in diced strawberries and strawberry jam.

Fry the Donuts:

Heat vegetable oil in a large pot to 350°F (175°C).

Fry donuts until golden brown, about 2 minutes per side.

Drain on paper towels and let cool slightly.

Fill the Donuts:

Using a piping bag, fill each donut with the strawberry cream mixture.

Finish and Serve:

Dust with confectioners’ sugar.

Top with additional diced strawberries if desired.