Preheat oven to 400F/200C.
Sieve the flour, salt, baking powder and sugar into a large bowl.
Rub the butter into the flour until it resembles breadcrumbs.
Slowly add the milk until you have a stiff dough. Don't add it all at once because you may not need it all and you'll end up with a sticky dough.
Roll the dough out into a rectangle about 30cm/12 inches long and about half as wide. Spread the mincemeat over the scone dough to make an even layer.
Working from the long side, roll up the mincemeat-filled scone rectangle like you were rolling a Swiss roll.
Brush the scone roll with the beaten egg.
Using a sharp knife or bench scraper, cut the scone roll into pieces about 2.5cm/1 inch thick. Place on a lined baking tray, leaving some room for the scones to rise.
Bake for around 12 minutes or until golden. Remove to a wire rack to cool.