1. Grate 2 tablespoons peel from tangerines. With a sharp knife, cut off remaining peel and white membrane from tangerines; discard peel and membrane. Working over a strainer set in a bowl, cut between inner membranes and fruit to release segments into strainer. You should have 2 cups segments; cover and chill. Discard membranes; save juice to use in step 2.
2. In a 3- to 4-quart pan, combine sugar, gelatin, grated tangerine peel, and 1 cup tangerine juice. Stir the mixture over medium-high heat until simmering. Remove from heat.
3. Beat remaining 2 cups tangerine juice with egg yolks to blend; stir into pan, then stir mixture over medium-low heat for 5 minutes.
4. Remove from heat and whisk in sour cream. Nest pan in ice water and stir often just until mixture begins to thicken, about 10 minutes. Lift pan from ice water, cover, and chill until mixture is firm, at least 1 1/2 hours or up to 1 day.
5. Spoon about 2 tablespoons tangerine segments into each glass (at least 12-oz. size). Stir cream mixture, then spoon about 1/3 cup over segments in each glass. Repeat to layer remaining tangerine segments and cream mixture equally in glasses.