A bakery classic in Eastern Europe, these lip-smacking treats combine a sweet yeast-based dough with a jam filling and a sugary glaze. They're usually shaped into rounds or, like in Martha's version, bowties.
In a small bowl, stir together yeast and sour cream. Let stand until yeast dissolves, about 10 minutes. Whisk in eggs until smooth.
In a large bowl, whisk together flour, granulated sugar, and salt. Using a pastry cutter or two knives, cut butter into dry ingredients until mixture resembles coarse meal. Stir in yeast mixture. Knead in bowl a few times until dough is smooth and comes together. Wrap dough in plastic and flatten into a square. Refrigerate at least 30 minutes.
Preheat oven to 400 degrees. On a lightly floured surface, roll out dough 1/4 inch thick. Using a 3-inch square cutter, cut out squares. Transfer to two parchment-lined baking sheets, spaced about 1 1/2 inches apart.
Place 1 teaspoon jam in the center of each square. Fold upper-right corner over filling, about two-thirds of the way toward opposite corner; press down to seal. Brush lower-left corner with egg wash, then fold corner up and over first fold, pressing down to adhere. (Be careful not to fold too tightly, or you may force out some of the filling.) Repeat with remaining squares.
Bake until edges are golden, 12 to 15 minutes. Let cookies cool on sheets on wire racks 5 minutes, then transfer cookies to racks to cool completely.
In a medium bowl, whisk together confectioners' sugar and butter. While whisking, drizzle in milk, a little at a time, until glaze has a runny consistency. Using a spoon, drizzle glaze over cookies. Let stand until set, 1 hour. Glazed cookies can be stored in an airtight container at room temperature up to 2 days.