Start by making the honeycomb butter. Tip the honeycomb into a freezer bag, twist the end to prevent any escaping and crush the honeycomb using a rolling pin. Cream the butter and vanilla bean paste in a stand mixer until really soft.
Add the crushed honeycomb and mix again until combined.
Lay a piece of cling film or baking parchment on the work surface and spoon the butter down the middle to form a rough sausage shape. Wrap up the butter tightly to make a smooth log, twist the ends to seal and put in the fridge to harden until needed.
Preheat the oven to 200°C/ Fan 180°C/ Gas 6. Sift the flour, baking powder and a pinch of salt into a large mixing bowl. Add the chilled, diced butter and rub into the dry ingredients using your hands.
When the mixture resembles sand and there are only very small pieces of butter remaining, add the caster sugar and mix to combine.
Make a well in the middle of the mixture, add the buttermilk and blueberries and stir to combine using a rubber spatula. Once the dough starts to come together, use your hands to form a rough ball.
Tip the dough out onto a lightly floured work surface. Very lightly knead for about 30 seconds to bring the dough into an almost smooth ball but do not overwork the dough.
Cut in half and flatten each half into a round disc each about 16 cm in diameter. Using a long, sharp knife cut each disc into 8 triangular wedge shapes.
Arrange the wedges on the prepared baking sheets and brush the tops with a little milk, scatter with demerara sugar and bake on the middle shelf of the preheated oven for 12-14 minutes, or until well-risen and golden.
Cool on a wire rack and serve slightly warm with slices of the honeycomb butter ready to spread on top.