In a small bowl combine yeast, water and 1 tablespoon sugar and let stand until foamy, about 5 minutes. In a large bowl whisk together remaining sugar, 4 cup flour, and salt and add yeast mixture, butter, milk, sour cream, and eggs, stirring until combined well. Stir in 3 cups flour and turn dough out onto a lightly floured surface. Knead dough 8 to 10 minutes, adding enough of the remaining cup flour to form a soft but slightly sticky dough. Form dough into a ball and transfer to a buttered bowl, turning to coat dough completely with butter. Let dough rise in warm place, covered with a kitchen towel, until doubled in bulk, about 1 hour. In a small heatproof bowl combine currants or raisins with boiling water to cover and let stand 20 minutes. Drain currants or raisins well. In a small bowl stir together sugar and cinnamon. Butter two 13- by 9-inch baking pans. Punch down dough and turn out onto a lightly floured surface. Divide dough into 4 pieces. Roll out 1 piece of dough into a 10-inch circle (about 1/4 inch thick) and cut into 12 wedges. Sprinkle each wedge with about 1 teaspoon currants and about 1/2 teaspoon cinnamon sugar. Beginning with outer, curved edge, roll up each wedge toward tip and curve ends gently to form a crescent. Transfer crescent, tips down, to a baking sheet and form more crescents with remaining dough and filling in same manner. (Crescents should be arranged in 3 rows of 8 in each pan for a total of 48.) Cover each pan with a kitchen towel. Let crescents rise in a warm place until almost doubles in bulk, about 1 hour. Preheat oven to 350°F. bake rolls in middle of oven 20 to 25 minutes, or until golden brown. Serve rolls warm.