Put the warm soy milk in a small bowl and sprinkle in the yeast, bread improver, and one tablespoon of the caster sugar. Stir and let sit for 10 mins.
Sieve the flour, cinnamon, and salt together into the bowl of a standard mix master with a dough hook attachment. Add the remaining sugar along with the butter, vanilla, and pink food colouring (if using.) Pour in the yeast and milk mixture.
On medium speed, knead for 10 to 15 minutes. Keep an eye on your dough. If it's not coming together and it's too dry, add more soy milk. If it's too wet, add more flour. Your dough should come together smoothly, and there should be no sticky, shaggy pieces left on the inside of the mixing bowl. To test if dough is ready, pause the mixer and roll a small amount into a ball using your hands. Slowly pull the ball apart and if it’s slightly transparent in the center, without the piece breaking, your dough is ready. This is called the ‘window test’. Once your dough has reached this consistency, remove from the bowl and gently place onto a floured pastry mat. Spread the dough out slightly so you can fold it in half again. Add half of your raspberries into the middle of the dough and fold it over. Return the dough to your mixer and add 2 tablespoons of flour. Mix on a low speed until the raspberries are fully incorporated into the dough. Do the window test again to make sure your dough is ready.
Place your dough into a large bowl that has been lightly oiled. Cover loosely with a kitchen towel and allow it to proof for at least 2 to 3 hours in a warm part of your kitchen. Your dough should double in size. For best results, leave the dough to rest overnight.
Once it's risen, punch it down a few times with your fist. Add the remaining raspberry pieces and then knead it again for a few minutes until combined.
Divide into 8 or 12 equal portions, depending on your preferred size, and knead each one lightly. Use a scale to measure them more accurately by weight..
Line a large baking tray with parchment paper and lightly grease.
Place the dough balls onto your baking tray, allowing the buns to just barely touch. Cover and let them sit for another 30 to 60 minutes.
Meanwhile, prepare the glaze by mixing together your boiling water and glucose syrup until it’s dissolved. Using a pastry brush, brush the tops of your buns with the glaze. Save any excess for brushing once more after baking.
For the topping, mix together the water, flour, raspberry powder, and food colouring into a paste. Transfer the mixture into a small piping bag and snip off a small corner. Pipe crosses onto the buns by drawing a long vertical line down the middle of the first row, from one end of the batch to the other. Repeat, and then do this horizontally to form crosses.
Preheat a convection oven to 180°C / 350°F and place a large heatproof dish filled with water onto the bottom shelf.
Bake for 15 minutes, then rotate your pan and bake for another 10 minutes, until the buns sound hollow when tapped.
Take the buns out of the oven and transfer to a rack to cool. Brush again with remaining glaze. Sprinkle any remaining freeze dried raspberries on top.
Serve warm your favourite vegan butter!