Adjust oven rack to lower-middle postion and preheat oven to 400 degrees F.
In a medium bowl, mix flour, 1/2 cup sugar, baking powder, baking soda and salt.
Grate butter into flour mixture on the large holes of a box grater.
Use your fingers to work in butter very lightly (mixture should resemble coarse meal), then stir in raisins.
In a small bowl, whisk sour cream and egg until smooth.
Using a fork, stir sour cream mixture into flour mixtureuntil large dough clups form.
Use your hands to press the dough against the bowl into a ball. The dough will be sticky in places, and there may not seem to be enough liquid at first, but as you press, the dough will come together.
Placee on a lightly floured surface and pat into a 1-8 inch circle about 3/4 inch thick.
Sprinkle with remaining 1 tsp sugar.
Use a sharp knife to cut it into 8 triangles.
Place on a cookie sheet, lined with parchement paper, about 1 inch apart.
Bake until golden, about 15-17 minutes.
Cool for 5 minutes and serve warm or at room temperature.