Babka buns with Nutella and tahini filling

Method

1. Gently warm the milk and 40g of the butter in a small saucepan until the butter has just melted (don’t let it boil). Put both flours, the salt, sugar and yeast in the bowl of a stand mixer (or in a large mixing bowl), then stir to combine. Make a well in the middle of the flour and pour in the warmed milk/butter and one of the beaten eggs, then mix with a wooden spoon to combine.
2. Mix in the stand mixer (or in the mixing bowl using an electric mixer) on medium speed for 15 minutes or until you have a smooth but wet and sticky dough. Turn the speed up slightly and add the remaining 100g butter, a tablespoon at a time, making sure each addition is incorporated into the dough before adding the next. Mix for 5 minutes more until the dough is smooth, slightly sticky and very elastic.
3. Cover the bowl, then leave the dough to rise in the fridge overnight (see Make Ahead).
4. For the filling, mix the Nutella with the tahini and allspice in a medium bowl. Dust the work surface well with flour, then tip out the dough and dust that with flour, too. Roll out to a rough 30cm x 60cm rectangle, moving the dough a few times during rolling to prevent it sticking. Dust with extra flour as necessary. Spread the filling evenly over the dough. Starting from a long edge, roll up the dough tightly like a swiss roll.
5. With the seam underneath, cut the dough into 6 equal pieces. Roll each piece so it’s slightly longer, then make a cut lengthways down the centre of each piece, leaving 1cm at one end so the halves are still just attached. Twist the 2 strands around each other in a loose knot, then put each one in a baking paper-lined Yorkshire pudding hole. Cover loosely, then leave in a warm place to prove for 30 minutes. Heat the oven to 180°C/160°C fan/gas 4.
6. Brush the tops of the buns with the remaining beaten egg, then bake for 25 minutes. Brush again with the beaten egg, cover with foil to stop the buns browning too much, then bake for 10 minutes more or until the buns feel springy to the touch. Leave to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely. Eat while still warm or as fresh as possible.