Simmer the milk in a small pan with the butter until the butter has melted
Sift both flours into a large mixing bowl (stand mixer bowl), then stir in the milk mixture and mix in with a wooden spoon to fully combine
Mix in the dough in the stand mixer or hand electric mixer for about 15 minutes, on medium speed, until you have a wet but sticky dough
Turn the speed up and slowly add the remaining 100g of butter, a tablespoon a table. Make sure the butter is fully incorporated in the dough before adding another spoon full
Mix for 5 more minutes until the dough is smooth, then cover the bowl and leave in the fridge overnight to rise
For the filling, mix the tahini with the Nutella in a bowl
Dust your work surface, then work your dough to create a flat rectangle shape, around 30 x 60 cm - making sure it does not stick to the surface
Spread the Nutella mixture over the dough, then roll the dough tighly like a swiss roll starting from the long edge
With the seam underneath, cut the dough into 6 pieces. Roll each piece out so it is a little longer. Then make a cut down the centre of each piece, leaving about 1cm at one end so the halves are still attached
Twist the 2 strands to create a knot then place each piece in a baking paper-lined Yorkshire pudding hole
Once all buns are done, cover with a towel and leave to proof in a warm place for a further 30 minutes
Heat your over to 180C
Brush the remaining beaten egg onto the buns, then bake for 25 to 30 minutes. Brush again with the beaten egg, cover with foil to stop the buns browning too much, then bake for 10 minutes
