Line a rimmed baking sheet with parchment paper and spray with cooking spray.
In a medium bowl, whisk together flour, sugar, baking powder, and salt. Using hands, rub butter into flour mixture until large crumbs form. Stir in sultanas and cherries. Stir in egg, milk, and vanilla extract until dough comes together.
Using a levered 2 ½-tablespoon scoop, drop dough, 2 inches apart, onto prepared baking sheet. Freeze for 30 minutes to minimize spreading during baking.
Meanwhile, preheat oven to 350°F.
Bake until golden brown, 20 to 25 minutes. Serve warm or at room temperature.
Recipe by TeaTime Magazine at https://teatimemagazine.com/rock-cakes/