Method

Make the dough:

• In a small bowl, combine the warm milk, yeast, and sugar. Let stand for 5 minutes, or until the yeast is foamy.
  
  
• In a large bowl, whisk together the egg, melted butter, flour, and salt.
  
  
• Add the yeast mixture to the dry ingredients and stir until a dough forms.

   

• Turn the dough out onto a lightly floured surface and knead for 5-7 minutes, or until smooth and elastic.

   

• Place the dough in a greased bowl, cover with plastic wrap, and let rise in a warm place for about 1 hour, or until doubled in size.

   

• Punch down the dough and divide it into 12 equal pieces. Roll each piece into a ball.

   

• Heat about 1 inch of oil in a deep fryer or large pot to 350°F (175°C).
  
  
• Fry the dough balls in batches for 2-3 minutes per side, or until golden brown.
  
  
• Remove the doughnuts from the oil and drain on paper towels.

Make the filling:

• In a saucepan, whisk together the milk, sugar, egg yolk, cornstarch, and vanilla extract.
  
  
• Cook over medium heat, stirring constantly, until thick and bubbly.
  
  
• Remove from heat and let cool slightly.
  
  

Fill the Doughnut:

• Make a small slit in the side of each doughnut and fill with the cooled custard.
  
  

Coat the Doughnut:

• Roll the filled doughnuts in a mixture of sugar and cinnamon.

Enjoy your delicious Bolas de Berlim!