Process the flour, baking powder, sugar, butter and 1teaspoon salt in a food processor until crumbly. Add the beer and process in bursts to form a soft dough.
Preheat the oven to 210°C (415°F/Gas 6–7). Turn the dough out onto a well-floured surface and knead until smooth, adding extra flour if needed. Divide the dough into four balls, place on greased oven trays and flatten slightly. Brush with a little water and slash the tops with a knife.
Transfer to the oven and bake for 10 minutes. Reduce the oven to 180°C (350°F/Gas 4) and bake for 10 minutes, or until cooked. Cool on a wire rack and serve with butter.