Make dough: in a medium bowl, whisk together flour, sugar, baking powder, and salt. Add butter and mix with a pastry cutter or your fingertips until butter is the size of peas. Stir in currants and lemon zest. Slowly drizzle in cream and mix with a fork just until dough begins to come together.
Turn dough out onto a lightly floured work surface; knead to bring dough together. Pat out to a 1/2-inch thickness. Using a floured 3-inch round cookie cutter, cut out circles of dough and transfer to a parchment-lined baking sheet, spacing 2-inches apart. Press together excess dough scraps and cut out more rounds. Freeze 15 minutes.
Preheat oven to 375°F. Brush tops of scones with more cream and sprinkle with sugar. Bake until set and lightly browned on top, 18 to 22 minutes. Let cool slightly on pan.
Make butter: in a small bowl, stir together butter, maple syrup, and salt until smooth. Serve alongside warm scones.