Place the vegan butter, sugars and vanilla extract into the bowl of a stand mixer fitted with the paddle attachment and cream the ingredients together until very light and fluffy (around 3-5 minutes).
While the butter and sugars cream together, place the psyllium husk powder in a small bowl and add the water. Mix well and then immediately add it to the butter mixture. Beat for a further minute to make sure the psyllium is completely combined.
In a separate medium bowl mix together the flour, cocoa, baking powder, baking soda and fine sea salt. Stop the stand mixer before adding the flour mixture and reduce the speed to low. Beat until just combined and do not overwork the dough.
Remove the bowl of the stand mixer and add 100g of the chocolate chips (reserve the remaining 40g). Mix until just combined.
Using a large cookie scoop, portion out 12 or 14 balls of cookie dough to match the number of peanut butter balls you made. Remove the peanut butter filling from the freezer.
Take one ball of cookie dough and make a well in the middle with your thumb. Press the frozen peanut butter filling into the centre and then tuck the sides of the ball of cookie dough down to cover the peanut butter completely (there should be no peanut butter showing!). Top the ball of dough with a few of the reserved chocolate chips and a tiny pinch of flaky sea salt before placing it onto the lined baking sheet with the remaining frozen PB filling. Repeat until every ball of dough is stuffed with PB filling and the tray is full of balled cookie dough.
Place the tray of cookie dough into the fridge to chill for at least 30 minutes and preheat your oven to 165c/340f (fan). Alternatively, place the cookie dough into an airtight container and freeze until you're ready to bake or for up to 2 months.
When you're ready to bake, line a new baking tray with baking parchment and arrange balls of chilled cookie dough evenly spaced apart.
Bake the cookies for 9 minutes. Working quickly, remove from the oven and carefully give the tray 5 sharp taps on the counter then immediately place it back into the oven for the remaining 4 minutes. Once baked, remove from the oven and allow to cool on a wire cooling rack for at least 20 mins or while you bake your remaining cookies.