In a large mixing bowl, place 2 cups self-rising flour, 1 teaspoon baking powder, ¼ cup sugar and ⅛ teaspoon salt.
Stir to mix and scatter 4 tablespoons unsalted butter, cold and in pieces, on top.
Using your fingertips or a pastry cutter, rub the butter into the flour until the mixture looks like coarse crumbs. A few pea-sized bits of butter are fine; they’ll help the scones be flaky. Work quickly so the butter stays cold.
In a small bowl, stir together ⅓ cup regular sour cream with ⅓ cup milk until combined.
Make a well in the center, add the wet ingredients, and mix just until combined. Integrate with the flour using a fork or spoon. It will be floury and irregular.
Fold in ½ cup raisins while there are still some floury patches.
Transfer to a clean counter and gather with your hands, turning the dough onto itself a few times until you can pat a rectangle about ½ inch thick. It won’t be a smooth dough like for a pie. Avoid kneading much; scones should be handled as little as possible.
Cut into rounds with a medium plain round cutter and place on a greased baking sheet. Use a plain round cutter (not fluted), and press straight down without twisting. Twisting seals the edges and prevents the scones from rising as high. Push down, lift up, done. If the cutter sticks to the dough, dip it in flour and shake off excess before you push down. Gather the scraps and re-pat once, touching as little as possible. The second-round scones will be slightly less tender than the first, but they'll still be very good.
Chill in the refrigerator for 20-30 minutes. Preheat oven to 350°F (180°C) while scones are chilling.
For the egg wash, mix 1 egg and 1 tablespoon milk in a small bowl and brush the tops of the scones. You can sprinkle some extra sugar for crunchiness and sweetness.
Bake for about 15-20 minutes, until puffed and lightly golden. Eat warm on their own, with butter, sour cream, clotted cream or jam.
Notes
Preheated oven: this is non-negotiable. Scones need the first spring that the hot oven provides. If you forgot to turn it on, leave the cut scones in the fridge or freezer while the oven preheats to the correct temperature.