In a large mixing bowl, combine all-purpose flour, salt, and granulated sugar. Create a well in the center and pour in warm milk mixed with dissolved fresh yeast. Let this mixture sit for 5-10 minutes until foamy. Add sweet butter and eggs, then knead the dough for about 8 minutes until it’s smooth and elastic.

Transfer the kneaded dough to a greased bowl and cover it with a clean kitchen towel. Place the bowl in a warm area and allow it to rise for approximately 90 minutes, or until the dough has doubled in size.

Once the dough has risen, gently punch it down to release excess air. Roll it out on a floured surface to about ½ inch thick. Use a round cutter to create circles and place them on a lined tray. Allow the cut dough to rest for another 10 minutes.

Heat vegetable oil in a deep pot or fryer to 350°F (175°C). Carefully drop the dough rounds into the hot oil, frying them for approximately 3-4 minutes on each side until they turn golden brown and puffy.

In a saucepan, heat whole milk over medium heat. In a separate bowl, whisk together egg yolks, sugar, and cornstarch until smooth. Gradually add the hot milk mixture to the egg mixture while whisking constantly. Return this mixture to the heat, stirring until it thickens, then stir in the vanilla extract.

Once the custard is cool, transfer it to a piping bag fitted with a round tip. Fill each bombolone with the creamy custard filling through the side. Lightly dust the tops with powdered sugar, and they are ready to serve.