Preheat the oven to 180°/160° fan/350°F/gas 4. Sift together the flour, baking powder and sugar. Rub the butter through the dry ingredients until you obtain a fine crumb texture. Whisk the egg and yogurt together until smooth, and making a well in the centre of the dry ingredients, pour in two thirds of the yogurt. Use a fork to stir gently until you obtain a stiff dough: you may need to add a few more spoonfuls of the yogurt mix.
When most of the dry ingredients are incorporated into the dough (there should be about 3 tablespoons of dry crumbs in the bottom of your bowl), tip everything out onto your worktop, and fold the dough onto itself until all the dried bits are mixed in. It is very important not to over-mix the dough. Folding the dough onto itself will incorporate the leftover dry ingredients and prevent over-kneading.
Roll out the dough until it is about 1.5cm thick - you may need to lightly flour your table and the top of the dough. Use a 5cm round cutter to form your scones.
Place the scones on a lined baking tray and, if there is any of the yogurt mix left over, brush the top of each scone with it, ensuring it doesn’t dribble down the sides.
Bake for about 12-15 minutes, or until well-risen and golden brown. Serve warm with clotted cream and jam.