Pre-heat the oven to 425°F (220°C). Line a baking sheet with baking parchment.
Cut 8 TBS (115g) of butter into very small pieces.
In a large bowl stir together the flour, baking powder, sugar, salt and baking powder and then add the cold butter. Squeeze the butter pieces between your thumb and fingers to flatten them. *See note below.
Pour in 3/4 cup (170ml) of the cold buttermilk and stir to form a loose, crumbly dough.
Dump the dough on to your work surface. Notice the pieces of butter showing and not all the flour has been incorporated yet.
Gather the dough together to form it into a somewhat cohesive mass. If you have a bench scraper it will help make this stage easier. Otherwise, working quickly, just use your hands. It won't come together completely and will still be a little crumbly.
Roll the dough into a rectangle 1/2" (12mm) thick and about 11" x 7" (28 x 18cm) and use your bench scraper or the edge of your hand to even out the edges. With the long edge of the rectangle facing you, fold the right 1/3 of the dough onto itself. Then fold the left 1/3 over as you would a business letter. Roll the dough out to 1/2" (12mm) thick again and do the letter fold as before.
Repeat the rolling and folding once more but this time roll the dough out to 8" x 4" (20 x 10cm)" and about 1" (25mm) thick. You can see the dough has come together quite nicely after the 3rd roll and fold. Pat the dough into a neat rectangle and removing as little as possible trim the edges with a sharp knife. Trimming the edges will allow the biscuits to rise evenly and to their full height in the oven.
Again, using a sharp knife, cut the dough into 8 more or less equal pieces. Place the biscuits on the prepared baking sheet. Gather the trimmings and form them into a loose round and set it on the baking sheet too. (That will become the baker's treat.)
Melt the remaining 2 TBS (25g) of butter and use it to brush the tops of the biscuits.
Bake for about 15 minutes until well risen and golden brown on top, rotating the pan half way through to ensure even baking.
Cool on a wire rack. Notice the flaky layers created by the rolling and folding (laminating) process.