Preheat oven to 400° Fahrenheit or 200° Celsius and prep a baking sheet with parchment paper or a baking mat.
Combine the diced apple, cinnamon, and Rumtopf (or rum) and set aside, stirring occasionally.
60 milliliter Rumtopf liquids, 1 teaspoon ground cinnamon, 100 grams apple
Whisk together the flour, sugar, baking powder, and salt in a large bowl. Grate the cold butter. Add the grated butter to the flour mixture and combine using your hands or a pastry cutter or forks until the dough looks like small crumbs. Transfer to the fridge or freezer while you assemble the wet ingredients.
250 grams flour, 75 grams sugar, ½ teaspoon salt, 2 ½ teaspoon baking powder, 115 grams butter
Whisk together the egg, buttermilk, and vanilla and drizzle over the dough crumbs. Do the same with the Rumtopf-apple mixture.
60 milliliter buttermilk, 1 teaspoon pure vanilla extract, 1 large egg, 60 milliliter Rumtopf liquids, 100 grams apple, 1 teaspoon ground cinnamon
Knead together the dough using your hands until it's just combined, then transfer onto a floured work surface.
Flatten into an 8-inch (20 cm) round disk. The circle does not need to be perfect - the less you handle the dough, the better. Cut the dough into 8 wedges and transfer to a baking sheet.
Do NOT skip this step. Transfer the cut wedges to the fridge or freezer for 15 minutes. This is to cool the butter back down, so your scones will stay neat and flaky, and won't spread as much during baking. You could also make the scones the night before, then bake directly from the fridge or freezer the next morning.
Bake on the middle rack for 18 to 26 minutes or until edges are golden brown and tops are starting to brown. Remove from oven.
For the Rumtopf glaze, combine the powdered sugar and Rumtopf liquids (or rum) using a fork, then drizzle over the scones.
25 grams powdered sugar, 1 teaspoon Rumtopf liquids