Preheat the oven to 160°C and line 2-3 baking trays with baking paper.
In the bowl of your stand mixer with the paddle attachment fitted, add the dairy-free butter, vanilla, brown sugar and white sugar and mix until combined. Add in the egg and extra egg yolk and continue to mix until smooth.
Add the flour, bicarbonate of soda and salt and mix on low until a soft cookie dough forms. FInally, add most of the chopped up chocolate, saving a few pieces to press into the top of the cookies before baking, and mix through to combine.
Using a spoon or cookie scoop, place 4 tablespoons of dough per cookie on the sheet making sure there is plenty of room for the cookies to spread (when baked these cookies will be approx 12 cm in diameter), and gently press a few extra chocolate chips or pieces into the top of the cookie dough.
Bake the cookies for approx 18 minutes, stopping half way to remove the tray from the oven and bang it a few times on the counter to deflate any extra air. Once the cookies are baked, again bang the tray a few times on the counter, and then use a spoon to gently shape the edges if you want your cookies to look perfectly round. Allow the cookies to cool on the tray to firm up before transferring to a wire rack to cool completely. Sprinkle with flakey sea salt for that little bit extra if desired.