In large mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add sour cream and egg yolk. Beat until combined. Using a wooden spoon, stir in flour until combined. (Dough will be sticky.) Divide dough into fourths. Cover and chill for at least 1 hour or until dough is easy to handle.
In a small bowl, combine sugar, chocolate pieces and cinnamon; set aside (or if desired, make Apricot-Walnut Filling).
On lightly floured surface, roll one-fourth of the dough into a 10-inch circle. Spread 1/4 of the filling over circle. Cut dough into 12 wedges. Roll up each wedge, starting at wide end. Repeat with remaining dough and filling.
Place cookies, tip sides down, about 2 inches apart on foil-lined cookie sheets. Bake in a 350 degree oven for 20 minutes or until golden brown. Transfer to wire racks to cool. If you like, sprinkle with powdered sugar.
Store in an airtight container at room temperature for up to 3 days, or freeze in freezer container for up to 3 months.
In a small saucepan, combine apricots, sugar and water. Bring to boiling. Reduce heat and simmer, uncovered, for 5 minutes or until thickened, stirring occasionally. Remove from heat; cool. Stir in walnuts.