Into the bowl of your stand mixer, add the yeast, castor sugar, and lukewarm buttermilk. Allow the mix to stand for 5 minutes and the yeast will begin to foam.
Add in the beaten eggs and mix until well combined.
Add in the Spelt flour, xanthan gum, ground cinnamon, and salt. Knead for 5 minutes on low speed and then increase the speed and mix for a further 5 minutes or until you are left with a soft, smooth, and elastic dough(Please note the dough will be smooth but it will be sticky to the touch). Add the softened butter cubes and knead for a further 5-7 minutes or until you have a soft and homogenous dough. The dough will be very slack after the butter is added but fear not because as you knead the dough, it will result in a soft, smooth, and shiny dough. Once the butter is incorporated, stop kneading as overbeating will result in compact brioche buns.
Add in the chocolate chips and dried cranberries. Knead for 3 minutes on low speed until the chocolate chips and cranberries have been well incorporated into the dough. (Please note the dough will be smooth but it will be sticky to the touch). Cover the dough with plastic wrap and allow it to rise for 1 hour at room temperature, before placing it into the fridge to rest overnight. The brioche can be made after 10–12 hours of resting. (Please note that the dough can rest for up to 3 days in the refrigerator before use.) Remove the dough from the fridge and turn it out onto a lightly floured surface. Deflate the dough and divide it into 12 equal pieces (I prefer to weigh the dough balls as this ensures that the buns bake evenly).
Roll each piece of dough into a smooth ball and arrange, seam side down, on a baking tray or in a baking dish, depending on your preference.
Cover and allow the dough to rise for 1½ – 2 hours or until the dough rounds have doubled in size.
Preheat the oven to 180℃ and then prepare the mixture for the crosses by combining the flour and water until you have a thick smooth paste. Spoon the paste into a piping bag. (If you do not have a piping bag, place flour paste into a ziplock bag and cut off the tip of one end of the bag). Pipe a line along each row of buns and repeat in the opposite direction to create crosses.
Bake the buns for 20-25 minutes or until golden brown.
While the buns are baking prepare the glaze by heating the castor sugar and water in a small saucepan. Bring to a boil and simmer for 2-3 minutes. Remove the buns from the oven and immediately brush the hot glaze over the top of the warm buns. Place the buns onto a wire rack and allow them to cool ~ If you prefer them hot out the oven, then go ahead and enjoy them piping hot.