Place the flours, salt and yeast into a food processor and briefly pulse together until blended.
Place the sugar and cardamom pods into a coffee grinder, blender or pestle + mortar and grind until fine. Add the cardamom sugar to the food processor. Cut the butter into 6 large chunks and scatter over the flour. Pulse in 3 times. Whisk together the egg, water and milk then pour into the food processor. Pulse together until a shaggy dough forms - you should still be able to see chunks of butter all over the place. Transfer the dough to a bowl and freeze for 30 minutes.
Roll the cold dough out on a floured surface into a 20-inch square. Fold the left third of the dough into the middle and then the right third into the middle so that it overlaps the other fold, like a business letter (see the .gif below the recipe). Rotate the dough 90-degrees clockwise so that the long edge is facing you and roll out again into a 20-inch square. Repeat the folding, rotating and rolling four more times (so you have completed a total of 5 fold and rolls) (see notes). Wrap the 20-inch square of dough in cling film and put it back into the freezer for 10 minutes.