Preheat oven to 425 degrees; grease a large baking sheet. In a large bowl, combine flour, sugar, baking powder, salt and cream of tartar. With a pastry blender, or two knives, cut in the butter until the mixture resembles coarse crumbs. In a small bowl, beat together the half and half and egg. Measure out and reserve 2 tablespoons of the mixture. Add remaining mixture to dry ingredients along with the raisins. Mix lightly with a fork until mixture clings together and forms a soft dough. Turn dough out onto a lightly floured surface and knead gently 5 or 6 times. Divide dough in half. With a lightly floured rolling pin, roll one half of the dough into a 7-inch round; cut into 4 wedges. Repeat with remaining dough. Place scones one inch apart on prepared pan. Pierse tops with the tines of a fork. Brush tops with reserved egg mixture. Bake for 15 to 18 minutes, or until golden brown. Serve warm.