Heat oven to 400 degrees. Combine sour cream and yeast in a small bowl. Set aside until slightly bubbly, about 10 minutes. Using a wooden spoon, stir in egg until smooth. Set aside.
Using two knives or a pastry cutter, cut butter into flour until it resembles coarse meal. Stir in sour-cream mixture until dough comes together.
On a lightly floured surface, roll out dough to 1/4 inch thick. Cut into 2 1/2-inch rounds. Transfer to ungreased cookie sheets, about 1 1/2 inches apart. Cover with a clean kitchen towel or plastic wrap. Let sit for 15 minutes.
Make a thumbprint in the center of each cookie. Fill each thumbprint with 1 teaspoon preserves. Bake until edges are golden, 12 to 15 minutes. Transfer pans to rack to cool. Let cookies cool on pans for 5 minutes. Remove cookies to rack. While cookies are still warm, drizzle with sugar glaze.