Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper. In a food processor, add the all-purpose flour, sugar, baking powder, and kosher salt. Cut in the cold, cubed unsalted butter until the mixture resembles coarse crumbs, about 15 to 20 seconds.

Blend in the cardamom extract, sour cream, and heavy cream to the crumbly flour mixture until the dough holds together but remains slightly crumbly; this should take about 30 seconds.

Transfer the dough onto the prepared baking sheet, shaping it into a disc approximately 1 inch thick. Cover it with plastic wrap and refrigerate for 30 minutes.

Once chilled, remove the dough from the fridge and cut it into 8 to 10 wedges. Brush the tops lightly with milk or cream and sprinkle cardamom sugar generously over the surface. Bake for about 18 to 20 minutes.

While the scones cool, whisk together powdered sugar, cardamom extract, and enough milk to reach a drizzling consistency. Once the scones are completely cool, drizzle the glaze over the top.