Preheat the oven to 190°C (374°F).
Cream together the butter and sugar until smooth.
Add the egg and mix well.
Sift in the flour, baking powder, and salt, and mix together.
Gently fold in the chocolate.
Shape the dough into balls, 90g each.
Place the dough balls on a baking sheet lined with parchment paper.
Bake in the oven for 12-13 minutes, then let cool before serving.