Preheat the oven to 180oC/Gas Mark 4 and line two large baking trays with baking parchment.
Add the vegan butter and sugar to an electric mixer and cream together, then add the peanut butter and vanilla and mix together until well combined.
Add the flour and salt, then mix on a very low speed until you reach a thick crumbly dough. If at this stage you are able to mix it into a rollable cookie dough, so what you have is a proper cookie dough instead of a crumbly dough, then you may not need to add any soy milk, but if you have crumbly dough then you will need the soy milk. (This usually depends on the moisture content of your brand of vegan butter and/or peanut butter so you can just judge this by eye. We used Flora Dairy Free and Proper Nutty and added all the milk, but you may not need to.)
Add a little of the soy milk as needed to get to a thick cookie dough that can be rolled into balls.
Add the chocolate chips and mix in. Roll into 16-20 big balls, then place onto the prepared trays.
Bake for 15 minutes until the tops are golden brown. The middles will still be very soft and wobbly; this is what you want so don’t be tempted to overbake – they will firm up as they cool!
Let the cookies cool and firm up on the baking sheet before moving them.