Step 1Place flour, sugar and salt in bowl of food processor, and place cut-up butter on top. Pulse to cut butter into flour until mixture is grainy and mealy. It doesn't matter if the mixture is a little uneven. (If doing by hand, break butter into flour using fingertips.)
Step 2Stir yeast, dash of sugar and water together in small bowl to dissolve yeast. Add to flour mixture, along with sour cream, 2 egg yolks and extracts. (Reserve egg whites for glazing.) Process mixture just until it forms a ball, 8 to 10 seconds. (By hand, stir to make sticky mass.)
Step 3Divide dough into 2 sections. Wrap in plastic wrap. Chill 20 minutes or overnight.
Step 4On lightly floured board, roll each dough section 1/8 inch thick, then trim into 12-inch circle. Smear each with 1/4 cup warmed apricot jam, then half of brown sugar, nuts and cinnamon. Cut into 12 wedges and roll from wide side to point into crescent shapes. Beat egg whites and brush crescents with them. Lightly sprinkle with about 1/2 teaspoon granulated sugar. Place on 2 baking sheets lined with parchment paper and place in 375-degree oven. Immediately reduce heat to 350 degrees. Bake until medium brown, about 20 to 25 minutes.