yolk, sugar and vanilla extract to first dough and mix thoroughly with a wooden spoon or paddle beater.
add butter gradually, mixing well.
add flour and salt and knead together into a soft dough.
knead in chopped chocolate, then continue to knead for about 5 minutes, until dough is soft and light. it will be quite soft and sticky.
scrape dough into a buttered bowl, cover with plastic wrap and let rise in a warm place until doubled – about 2 hours, depending on the ambient temperature.
put 24 cupcake liners into muffin pans.
punch down dough and pull off golf-ball sized pieces, roll them into balls and pop into cupcake liners.
cover loosely with plastic wrap 