Once the butter is soft and at room temperature, mix with a whisk until it turns pale.

Next add the sugar in bit by bit, while mixing well.

Add a beaten egg in 5 portions, mixing well after each addition. Be absolutely sure that you add it in bit by bit.

Mix well until it looks like this.

With a kitchen knife, chop up the chocolate into 5 mm pieces. Add it to the batter.

In a separate bowl, combine the flour and cocoa powder and sift.

Transfer the sifted flour into the Step 5 bowl and mix until there are no flour streaks.

At first it will be very floury, but gradually the dough will blend in. It's easier to use a wooden spatula instead of a rubber one.

This is what the dough looks like once it's well incorporated.

Line a baking tray with parchment paper and using a spoon, drop the dough onto the tray.

When you bake them, they will spread out so make sure to spoon the dough high.

Next, in a preheated oven at 350℉ (180℃) bake for 17 minutes till they are done.