When the dough is ready, pour out onto a floured surface and form into a rough ball. The dough might still be a little sticky, but just incorporate a touch more flour as needed.
Divide the dough into eight equal parts (use scales to ensure they are as close in weight as possible).
Taking one ball at a time, pinch the bottom together, and then roll it on a surface until you have a round ball.
Roll each ball out into a circle and place a chunk of chocolate in the middle.
Cover the chocolate with the dough, give it another little roll until it's as round as possible, then place in the centre of a greased, round springform pan (mine is 20cm / 8").
Continue with the remaining dough balls and place them around the ball in the centre (leaving a little space in between them).
Cover well with clingfilm and place in the fridge overnight.
The next morning, take the buns out of the fridge, cover them with a tea towel, and let them sit on the counter until they come up to room temperature.
Pre-heat the oven to 175℃ (350℉).
Beat the egg and then liberally brush over the top of the buns.
Bake for around 20 minutes, until the top is nice and golden.