In a wide fry pan; cook bacon over medium heat until crisp. Spoon off and discard all but 3 TBSP of the drippings; keep pan with bacon warm over lowest heat. In a 5 6 quart pan; cook pasta in three quarts boiling water just until tender to bite (@3 minutes for dry capellini. 8-10 minutes for dry vermicelli, and 1 to 2 minutes for fresh angel hair pasta); or cook according to package directions. After adding the pasta to the boiling water, spoon 1/2 c of the sour cream into each of 4 wide, shallow bowls; place bowls in a 200 degree oven while completing cooking. Drain pasta well; add pasta and chives to bacon in the pan. Mix lightly, using two forks. Spoon an equal portion of pasta mixture into each warm bowl. Make a nest in the center of each; slip in an egg yolk. Mix each portion individually and sprinkle with cheese.