Heat the milk in a saucepan and add the cardamon. Bring it just before the boil and then turn the heat off. Add the butter and leave to cool for a minute or so.
Mix the dry ingredients together into a large bowl and make a well in the centre. Crack in the egg and then add the milk mixture. Bring it all together to make a soft dough.
Keep it in the bowl and knead the dough until it is smooth and no longer sticks to your hands. Once the dough is ready, cover the bowl with a tea towel or cling film and leave somewhere warm for 30 minutes. You want it to double in size.
Make the gilling while you wait - simply beat the butter, sugars and salt together until its creamy and spreadable.
Tip the risen dough out onto a lightly floured surface and roll into a rough rectangle - about 35 cm x 20 cm roughly
Spread the butter mixture all over.
Roll it up dough tightly into a Swiss roll (by rolling along the longer edge). Make sure it’s sitting on its seam and then cut into 6 slices
Arrange these on a large baking tray - leaving good gaps between them and then cover with a tea towel and let them prove again for 30 minutes until they’re nearly doubled in size.
Preheat the oven to 200C
Brush the tops with beaten egg and Demerara sugar and bake for 25 minutes approximately - the should be lightly golden.
I serve mine with a simple icing made with icing sugar and water to loosen.