Preheat the oven to 160°C (325°F) and line 2-3 baking trays with baking paper.

In the bowl of a stand mixer fitted with the paddle attachment, add the dairy free butter, vanilla, brown sugar, and white sugar. Mix until well combined.

Add the egg and extra egg yolk, and continue mixing until smooth.

Add the flour, bicarbonate of soda, and salt. Mix on low speed until a soft cookie dough forms.

Stir through most of the chopped chocolate, reserving a few pieces to press into the tops of the cookies before baking.

Using a spoon or cookie scoop, portion 4 tablespoons of dough per cookie onto the prepared trays, leaving plenty of space for spreading. These cookies will bake to around 12 cm in diameter.

Gently press a few extra chocolate chunks into the top of each dough mound.

Bake for approximately 18-20 minutes, removing the tray halfway through baking to bang it gently on the counter. This helps to deflate any air for a chewier texture.

Once baked, bang the tray again on the counter to flatten the cookies slightly. If you want neat, round cookies, use a spoon to gently nudge the edges into shape while still warm.

Let the cookies cool on the tray to firm up before transferring to a wire rack to cool completely. Sprinkle with flaky sea salt if desired.