Melt the chocolate in the microwave or in a double boiler. If there are still a few lumps, stir the chocolate until they melt completely. Set aside.
In a mixing bowl, beat the butter and sugars together using a hand mixer till pale and fluffy. Add the egg and vanilla and beat again.
Now add the melted chocolate and peanut butter and beat on low speed to combine.
Sift the flour, baking soda, salt and cocoa into the bowl. Fold gently to combine till you have a thick, soft dough. Stir in the chocolate chips. Cover the bowl with clingfilm and chill for 30 minutes. I find this enough time for the dough to no longer be super sticky and of a scoopable consistency. Longer than this firms up the dough much more and you will need to keep it at room temperature for about 10 minutes to soften before you scoop. The longer you chill the dough, the thicker the baked cookies will be, so if you want thinner, crispier cookies, reduce the chill time.
When ready to bake, preheat the oven to 180 C. Line two baking trays with silicone mats or non stick baking paper.
Scoop the chilled dough into equal sized rounds (a medium 1.5 tablespoon cookie scoop is highly recommended for this dough) and place them two inches apart on the tray. Drizzle each with about a teaspoon of extra peanut butter.
Bake for 10 minutes or until the cookies still look puffy in the center (over-baking leads to drier cookies). Gently rap the baking tray on the counter to flatten the cookies, then set aside to cool and firm up for 10 minutes. While the cookies are still hot, press a few extra chocolate chips onto the tops for melty goodness, then transfer to a wire rack to cool completely.
To store, let the cookies cool completely, then keep then in an airtight tin for 4 to 5 days or in the fridge for a week and in the freezer for longer. Happy baking!