In a large bowl, rub the butter into the dry ingredients until the mixture resembles fine breadcrumbs.
Stir ¾ of the cheese into the mixture along with the salt and pepper.
Make a well in the centre. Break in the egg and pour in the kefir or buttermilk.
Stir with a round-bladed knife from the inside out until the mixture comes together.
Roll out into a rectangle about ¼ in / 1 cm thick.
Spread the pesto over the top in a thin layer, leaving a slight gap around the edges.
Roll it up as tightly as possible on the long side to form a log then slice into 8 pieces.
Lay the pieces out onto a lined baking tray and top with the remaining cheese.
Bake at 200℃ (400℉, Gas 6) for 20 minutes when the tops should be golden and the bottoms sounding hollow when tapped.
Don't worry if the mixture is a little sticky, just flour the rolling surface well.If you don't have cream of tarter, just omit this and the bicarbonate of soda and use 1 ½ tsp of baking powder instead.Please note: calories and other nutritional information are per serving. They're approximate and will depend on exact ingredients used.