For the dark cardamom rye dough, add the black treacle and muscovado sugar to 200ml/7fl oz warm water and stir well.
Put the flours in a large mixing bowl, add the cardamom and the yeast to one side of the bowl and the salt to the other. Use one hand to mix and the other to pour in three-quarters of the sweetened water. Add the olive oil and bring the dough together using your hands. Depending on the dough’s consistency, you may need to add the rest of the water – ideally the dough should be quite wet and sticky.
Lightly oil a work surface and turn out the dough. Knead for about 5-8 minutes, or until the dough is smooth and elastic. Shape the dough into a ball and place in a large bowl. Cover with cling film and set aside to prove for an hour, or until doubled in size.
For the orange rye dough, put the orange juice and zest into a measuring jug. Top up with water to make 200ml/7fl oz and stir to combine.
Put the rye and white flour in a large mixing bowl. Add the yeast to one side of the bowl and the salt to the other. Gradually pour about three-quarters of the orange juice mixture into the bowl, using your free hand to mix in the liquid. Add the olive oil and caster sugar.
Gradually bring the mixture together to form a fairly sticky dough, adding the remaining orange juice, if required. (You might find you don’t need all the fluids but you can adjust the quantity according to how the dough feels.)
Lightly oil a work surface and turn out the dough. Knead for around 5-8 minutes, or until the dough is smooth and elastic.
Shape into a ball and place back in the mixing bowl. Cover with cling film and set aside to prove for an hour, or until the dough has doubled in size.
Once both doughs have proved, knock them back and then roughly shape them into rectangles.
On a lightly oiled work surface, use a rolling pin to roll out each piece of dough into a rectangle approximately 30x20cm/12x8in. Try to make both rectangles of dough the same size.
Cut each rectangle in half to create two rectangles 30x10cm/12x4in. Layer them up on top of each other, starting with the orange layer, then cardamom layer and brushing each layer with a little with water to help them stick. Repeat until all the dough is used.
Pull the corners out so the dough is in a neat rectangle shape. Using sharp knife, slice the dough lengthways into 12 equally-sized strands about 2cm/¾in.
Roll each strand into a sausage about 20cm/8in long and then tie each strand into a knot shape and place on lightly floured baking parchment.
Gently cover the rolls with lightly oiled cling film and allow to prove for at least an hour.
Preheat the oven to 220C/425F/Gas 7.
Five minutes before the end of proving, pop two baking trays into the oven.
For the glaze, place the orange juice and the dark muscovado sugar in a small pan and heat gently until the sugar is dissolved. Simmer until a syrup forms. Set aside.
Once proved, remove the hot trays from the oven and slide the rolls onto them using the baking parchment. Put the baking trays in the oven as soon as possible. Bake for 10 minutes.
After 10 minutes, turn the oven down to 180C/350F/Gas 4 and bake for another 5-10 minutes. Check the rolls are ready by tapping their bottoms and listening. If it sounds hollow the rolls are ready. Transfer onto wire racks and brush with the glaze while still warm.
When cool, serve the rolls with a slathering of slightly salted butter.