Make the Donuts:

Prepare the Dough: In a large mixing bowl, combine the flour, yeast, sugar, and salt. Add the warm milk, eggs, and softened butter. Mix until a sticky dough forms. Knead the dough for 6–8 minutes (by hand or with a dough hook) until smooth and elastic.

Let It Rise: Place the dough in a lightly greased bowl, cover with plastic wrap or a damp towel, and let it rise in a warm place for 1–1.5 hours, or until it doubles in size.

Shape the Donuts: Roll out the dough on a floured surface to about ½-inch thickness. Use a heart-shaped cookie cutter to cut out the donuts. Re-roll scraps as needed.

Second Rise: Place the heart-shaped dough pieces on a parchment-lined baking sheet. Cover lightly and let them rise for another 30 minutes.

Fry the Donuts: Heat oil in a deep fryer or heavy-bottomed pot to 350°F (175°C). Fry the donuts in small batches, about 1–2 minutes per side, until golden brown. Transfer to a wire rack to cool.

Make the Vanilla Custard:

In a medium saucepan, heat the milk over medium heat until it begins to steam (don’t boil).

In a separate bowl, whisk together the sugar, egg yolks, and cornstarch until pale and smooth.

Gradually pour the hot milk into the egg mixture, whisking constantly to prevent curdling.

Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thickened. Remove from heat and stir in butter and vanilla. Cover with plastic wrap (directly touching the custard to prevent a skin) and chill until set.

Assemble the Donuts:

Use a piping bag fitted with a small round tip to fill each cooled donut with vanilla custard. Insert the tip into the side or bottom of the donut and squeeze gently until filled.

Caramelize the Sugar:

Sprinkle a thin, even layer of granulated sugar on top of each donut. Use a kitchen torch to caramelize the sugar until golden and crisp. Let the caramel set before serving.