1. Make the Dough:

1. In a small bowl, combine warm milk and yeast. Let sit for 5 minutes until foamy.
2. In a large bowl, mix sugar, melted butter, egg, and salt. Stir in the yeast mixture. Gradually add flour, mixing until a soft dough forms.
3. Knead the dough on a floured surface for 8-10 minutes until smooth and elastic. Place in a greased bowl, cover, and let rise in a warm place for 1-2 hours, or until doubled in size.

2. Prepare the Custard Filling:

1. In a medium saucepan, heat milk and cream over medium heat until steaming but not boiling.
2. In a separate bowl, whisk sugar, egg yolks, and cornstarch until smooth.
3. Slowly pour the hot milk mixture into the egg mixture, whisking constantly. Return the mixture to the saucepan and cook over medium heat, stirring, until thickened (about 2-3 minutes).
4. Remove from heat, stir in vanilla extract, and let cool. Cover and refrigerate until ready to use.

3. Shape and Fry the Donuts:

1. Roll out the dough to 1/2-inch thickness. Use a heart-shaped cookie cutter to cut out hearts. Place the hearts on a floured surface, cover, and let rise for 30 minutes.
2. Heat oil in a deep fryer or heavy-bottomed pot to 350°F (175°C). Fry the donuts in batches for 1-2 minutes per side, or until golden brown. Transfer to a paper towel-lined plate to cool.

4. Fill the Donuts:

1. Using a piping bag with a round tip, fill the donuts with the prepared custard by inserting the tip into the side of each donut.

5. Caramelize the Sugar:

1. Sprinkle a thin, even layer of granulated sugar over the top of each donut. Use a kitchen torch to caramelize the sugar until golden and crisp.

6. Serve and Enjoy:

• Let the caramelized sugar cool slightly to harden, then serve fresh.