FOR THE FILLING:
In a saucepan, mix the milk, egg yolks and butter.
Bring to a low heat for about 10 minutes or until a smooth and creamy consistency is achieved.
Remove from heat and stir in the vanilla essence and lemon juice.
Stir well until mixture is smooth and consistent.
Transfer to a bowl and set aside.
FOR THE DOUGH:
In a separate bowl, add the yeast, milk, and sugar and mix together. Let stand for 5 minutes to activate the yeast.
Add all ingredients except flour and mix well adding the flour gradually until the dough is easily shaped and kneaded. Mix until fully combined.
Form the dough into medium size balls (50 grams) and let them rest on a board sprinkled with flour.
Cover with a cloth and let sit for about 1 1/2 hour or until they ddouble n sizei.
Fry the bolas de berlim in a deep frying pan on high heat one by one about 1 /2 minutes each side ore until golden brown.
Place on a plate lined with paper towels to drain oil.
Once the Portuguese doughnuts are cooled, cut 3/4 of the way and fill with sweet egg filling.
Serve and enjoy!