Cream together the softened unsalted butter and powdered sugar until light and fluffy.
Mix in the sour cream until well combined.
Gradually add the wheat flour, stirring until a soft dough forms.
Wrap the dough in plastic wrap and refrigerate for at least one hour.
Preheat your oven to 350°F (175°C). Roll the chilled dough to about 1/8-inch thickness and cut into triangles.
Place a small spoonful of black currant jam at the wide end of each triangle and roll to form a crescent shape.
Arrange the cookies on a parchment-lined baking sheet and bake for 15-20 minutes, or until lightly golden.
Let them cool on a wire rack and dust with powdered sugar before serving.
