1. Melt butter in a small bowl over low heat.
2. Add butter and two types of sugar in a mixer bowl and beat well until fluffy.
3. Sift flour in a bassina and add baking soda.
4. Add egg, vanilla and pinch of salt in the mixer bowl.
5. Beat well in medium speed.
6. Add flour slowly and beat until mixture is homogenous.
7. Finally, add chocolate pieces and beat again.
8. Shape small balls of 30g each and bake in the oven at 180C for 10-11 minutes.