To make the buckwheat danish pastry dough:

1. Make the dough. Place the flour in a large bowl. Add the sugar and salt to one side of the bowl and the yeast to the other. Add the egg and ¾ of the milk. Combine everything with the blade of a knife and scrape the sides of the bowl so all the ingredients are incorporated. Slowly add the rest of the milk, if needed, to form a soft dough. Tip the dough onto a heavily floured surface and knead for 10 minutes. You should have a smooth ball of dough that is still a bit sticky. When you push the dough with a finger, it should spring back. Cover with plastic wrap and chill the dough for 2 hours in the fridge.

    

2. Roll out the dough and seal the butter block. With a rolling pin, roll the dough into a rectangle roughly 35*25 cm (13*8 inch), about 5mm (0.2 inch) thick keeping the edges straight. Put the butter between 2 sheets of parchment paper and beat it with a rolling pin until you have a rectangle half the size of your dough, around 18*12 cm (7*5 inch).  Place the pliable butter on top of half of the dough, fold the over half on top of the butter and seal the edges with a rolling pin.

    

3. Roll out the dough, fold it, and refrigerate.Roll the dough into a rectangle again, 35*25 cm (13*8 inch), about 5mm (0.2 inch) thick. If you can see some butter piercing through, put a little bit of flour on it. Then fold the dough into quarters by folding the two ends of the dough into the middle and then folding one half on top of each other as if clothing a book. Brush away any excess flour while folding. Cover in plastic wrap and refrigerate for 30 min.

    

4. Create more layers. Take the dough out of the fridge and place it horizontally on a lightly floured surface, making sure the edge where you can see the folds is the one directly facing you (check photos). Roll it into a 35*25 cm (13*8 inch) rectangle. Fold it into thirds this time by folding 1/3 of the dough over the center and fold the last third over the top.  Cover in plastic wrap and refrigerate for 30 min. Repeat this process of rolling (always make sure the fold side is facing you) into a 35*25 cm (13*8 inch) rectangle, folding  into thirds like a letter, and refrigerating the dough 30 min, 3 more times.

To shape the buns:

1. Make the filling. Combine all the ingredients in a bowl with a plastic spatula. It should be very soft and spreadable.

    

2. Spread the filling over the dough. Take the dough out of the fridge and turn it onto a large floured surface roll it into a 35*25 cm (13*8 inch) rectangle. Gently spread the filling all over the dough, ideally with a palette knife. Then fold one half of the dough on top of the other. There should be a layer of dough, a layer of filling in the center and another layer of dough on top.

    

3. Shape. Cut 8 vertical strips, about 2,5cm (1 inch) wide. Stretch them by twisting them with the palm of your hand. Then take one strip in your hand and wrap it around your index and middle fingers twice. Pinch the end of the strip in the center of the knot to hide it. Check out this very useful video to see someone do it.  Repeat to shape the other knots and place them on 1 baking tray lined with baking parchment, spacing them well apart because they will expand in the oven.

    

4. Prove the chocolate swirl buns. Cover and prove the dough overnight in the fridge or leave to rise for 1 hour at room temperature (it shouldn’t be too warm or the butter in the filling will melt).

    

5. Bake. Make the egg wash by whisking together the egg yolk and the milk in a small bowl. Brush the top of the buns with egg wash. Preheat your oven to 180°C (355°F)* and make the syrup while it heats up. Combine the sugar and water in a small saucepan, let it boil then reduce the heat and let it gently simmer until all the sugar has dissolved.  Bake the buns for 20 min or until golden brown. Take them out of the oven and immediately brush them with the syrup. Let them sit on the tray for 15 min then transfer them to a wire rack to cool down completely.