Preheat the oven to 177°C (350°F) fan or 197°C (386°F) conventional and line a few baking trays with baking paper.
Whisk the peanut butter, coconut oil, sugars and vanilla together in a large mixing bowl until combined.
Sift the flour, baking powder, baking soda and cornflour (starch) in to the wet ingredients and stir together until just combined. Add the milk a tablespoon at a time until the batter forms a thick cookie dough. How much milk you will need will depend on your peanut butter consistency. I generally find 2 tablespoons is perfect but you may find you need less.
Fold in the chocolate chips and then either scoop the dough into balls with a small ice-cream scoop or roll it into balls with clean hands.
Place the cookie dough balls on the prepared trays placing them around 2-inches apart. Pop the trays in the oven one at a time and bake for 10-13 minutes My happy place is between 11 and 12 minutes when the outer cookie is golden but the centre is still a little soft. The cookies will continue to cook after they are removed from the oven.
Remove the trays from the oven and allow the cookies to cool for at least 15 minutes. Repeat with your remaining cookie dough. Serve warm or cool.
Store in an airtight container for up to 3 days.