Add chopped chocolate and heavy cream to a heatproof bowl. Place it over a small saucepan of simmering water and stir while the cream heats and the chocolate melts. Remove it from the heat once it's nearly all melted, and continue stirring until it is smooth.

Place this in the refrigerator for 25-30 minutes, stirring regularly to chill it evenly.

Once the chocolate is cooled and beginning to firm up, dollop 16 mounds of the ganache on a sheet of parchment paper. Place this in the freezer for around 20 minutes.

Mix the butter and sugars in a large bowl using an electric mixer until the mixture is light and creamy. Add in the egg, followed by the vanilla.

Add the dry ingredients to the wet ingredients and stir them using a wooden spoon or rubber spatula until mainly combined, leaving a few streaks of flour. Mix in the chocolate chips

Portion the dough into 16 even pieces. 

Remove the ganache from the freezer. Take one piece of cookie dough and slightly flatten it in your palm. Place a piece of ganache in the middle, then tuck the sides of the cookie dough around it to enclose it. Roll it between your palms to make a ball. 

Continue with the rest of the dough and ganache. Try to touch the ganache as little as possible. It will melt again very quickly from the heat of your hands.

After rolling, place the cookie balls in the refrigerator for 15 minutes while you preheat the oven.

Preheat the oven to 350°F/180°C and line baking sheets with parchment paper.

Space the cookie balls at least 2 inches apart on the trays. Bake for around 12 minutes until lightly golden brown. The baking time will depend on your oven.

Let the baked cookies cool on the trays for around 5 minutes before transferring them to a wire rack for further cooling.