Preheat oven to 400º. Line 2 baking sheets with parchment paper and set aside. Whisk flour, sugar, and baking powder together in a large mixing bowl. Using a pastry cutter or 2 table knives, cut butter into flour mixture until it resembles coarse meal flecked with pea-size pieces of butter. Stir in sultanas. Add milk and stir until dough just comes together.

Turn dough out unto a lightly floured surface. Dust hands with four and gently knead with the heels of your hands several times until dough forms a rough ball. (Do not over knead dough, or scones will be tough.)

Divide dough into 20 equal pieces, gently shape each into rounds, and arrange on prepared baking sheets 1"-2" apart. Beat egg and 1 tsp. water together in a small bowl. Using a pastry brush, brush tops of dough rounds with egg wash.

Bake scones until golden brown, 30-35 minutes. Set aside to cool on wire racks for 5-10 minutes. Set aside to cool on wire racks for 5-10 minutes.

Serve warm with butter and marmalade or jam.