Melt the butter, pour it into a bowl, add the 2 types of sugar and stir.
Beat the eggs, add them to the bowl and stir once again with a whisk until fully absorbed.
Sift the flour, salt, vanilla and baking powder. Pour them into the bowl and stir vigorously with a wooden spoon until you obtain a thick, sticky dough.
Cut the chocolate into small pieces and add them to the dough; if using chocolate chips, add them in whole.
Stir the mixture with the spoon, cover with foil and put it in the fridge for 20 min.
Lay out a large, flat, wide tray with baking paper. Take the dough out, scoop from it with a spoon and form a ball using your hands. Your hands need to be slightly moist, so the dough doesn't stick to them.
Form the balls and arrange them in the tray with some space in between them (don't make them too large because the dough expands during baking). I got 12 large biscuits from the dough.
Heat the oven to 356°F (180 °C) with the fan on and put the tray in the middle of the oven.
Bake the biscuits 12-15 min. Keep an eye on them, once they start to change color and turn golden around the edges, take them out.
Place each biscuit onto a metal grid to cool. What you get is crunchy biscuits with a nice, soft inside and a saturated chocolate taste.