1 - In a small saucepan heat the butter, milk and salt until the butter is melted.
2 - Allow the mixture to cool until it is lukewarm.
3 - In a large bowl, stir together the flours, yeast, cardamom and sugar until combined.
4 - Make a well in the centre and crack in the eggs.
5 - Pour in the lukewarm milk mixture and stir everything together to form a sticky dough.
6 - You may have to use your hands as the dough becomes stiffer.
7 - Oil the work surface with a teaspoon of olive oil.
8 - Turn the dough out onto the oiled surface and knead vigorously for 5–8 minutes, using a plastic scraper as needed to prise the dough from the work surface.
9 - Don’t be tempted to add flour, as this will make the buns dry and tough.
10 - Keep kneading until the dough is considerably less sticky, smoother and more elastic.
11 - Shape into a ball, and put into a large, greased bowl.
12 - Cover the bowl with a clean tea towel and set aside in a warm place to prove for an hour, or until doubled in size.
13 - Meanwhile, for the filling and topping, mix the softened butter in a bowl with half the sugar and 1 tablespoon cinnamon.
14 - Use a fork to mix the sugar and spice into the butter until it is completely combined.
15 - Mix the remaining sugar and cinnamon in a separate bowl and set aside.
16 - When the dough has risen, turn out onto a floured work surface and gently roll out into a 36x24cm/14x9½in rectangle.
17 - Spread the cinnamon-sugar-butter evenly over the dough with a table or palette knife.
18 - With the longest edge closest to you, roll the dough up into a cylinder.
19 - Cut into 12 even slices.
20 - Place each slice onto a flattened out paper cupcake case on a baking tray, or into a greased muffin tin.
21 - (Baking in a muffin tin will make your cinnamon buns taller and domed.
22 - )
Cover with a clean tea towel and set aside to prove again for 30–45 minutes, or until risen.
23 - Preheat the oven to 200C/180C Fan/Gas 6.
24 - Brush the tops of the buns with beaten egg and dust liberally with the cinnamon sugar.
25 - Bake for 12 minutes until the buns are dark golden-brown.
