Preheat the oven to 220C/gas 7/fan 200C. Mix the flour, bicarbonate of soda and salt in a bowl. Add the butter, cut into small pieces and rub in with your fingertips until the mixture resembles fine breadcrumbs.
Tip in the buttermilk and mix lightly and quickly to form a soft dough. Knead very briefly, then roll out to 2cm thickness and cut into sixteen 5cm rounds.
Put on a baking sheet (no need to grease) a little apart, and bake for 12-15 minutes, until risen and pale golden.