Place the sultanas and raisins in a medium bowl. Add the rum and stir to coat. Add 75ml of just boiled water. Stir, cover and leave to soak.
Grind the psyllium husks into a sandy powder using a blender or a mortar and pestle. Place in a small bowl and mix in 6tsp water. Leave to thicken.
In a microwaveable bowl, place the vegan butter. Heat in the microwave until just melted. Add the milk and stir to combine. Add the yeast and whisk. Leave for the yeast to bloom for 5 minutes or until a little frothy on the surface.
In the bowl of a stand mixer fitted with a dough hook attachment, add the strong white bread flour, caster sugar and the thickened psyllium husk mixture. Add the yeast/milk mixture. Beat on low speed until the dough is combined and smooth but very sticky. Note that psyllium husks like to clump together, so you'll need to knead well to ensure they're incorporated throughout the dough.
Remove the dough hook and transfer the dough to another, medium bowl greased with a little neutral oil. Cover with reusable wrap or a damp tea-towel and leave to proof at room temperature for an hour.
While the dough proofs, crack open the cardamom pods and transfer them to a mortar and pestle. Grind them roughly.
Once the dough is proofed, return it to the bowl of the stand mixer and add the cardamom and other spices along with the orange zest and flaky sea salt. Drain the raisins/sultanas but reserve the liquid. Add the raisins/sultanas to the dough. Attach the dough hook and knead on low speed for a few minutes or until the fruit is all incorporated. If the fruit doesn't want to stay in the dough, transfer the dough to a clean surface and knead by hand instead. This should help.
Transfer the dough back to the oiled bowl, cover well and leave to proof for another hour.
Once proofed number 2 is over, It's time to shape the dough. Line a baking tray with baking parchment and set aside. Transfer the dough to a clean surface and push out any large air bubbles with your finger tips.
Using a bench scraper or sharp knife, cut the dough into 15 portions. If you'd like to be accurate, you can weigh the dough. When I made these, each bun weighed 90g.
Once the dough is divided, take one piece of dough and gently push it into a flat square with your fingertips. Fold the edges over to make a little pouch shape and then flip upside down to the smooth side is facing up and the folded side is on the counter. Make your hand into a concave dome and place over the dough. Move your hand in a circular motion, applying light pressure to the ball of dough beneath. This should form a ball of dough with a tight, smooth surface. Place the ball of dough on the tray and repeat the process with the remaining portions of dough. Ensure the balls of dough are evenly spaced apart.
Cover the balls of dough and leave to proof for their third and final hour. 30 minutes into their final proof, preheat the oven to 200c and prepare the mixture for the cross.