Instructions

1. 1
   Select one or more molds. The total volume will be approximately 8 cups; a ring mold, 2–3 glass containers (as pictured), or any other assortment should work; for best results, the container should be at least 3 in (10 cm) deep, allowing for about ten 1cm-thick layers.
2. 2
   Stir 1¼ cups boiling water and one package gelatin in a small bowl for at least 2 minutes, until completely dissolved. In practice, it may not quite completely dissolve.
3. 3
   Pour ¾ cups dissolved gelatin into the mold(s).
4. 4
   Refrigerate for about 15 minutes, until the gelatin sets but is not yet firm: the gelatin should stick to your finger when you touch it. The aim is for the layers to stick, but not mix.
5. 5
   Refrigerate the remaining gelatin for about 5 minutes, until it is slightly thickened (to the consistency of unbeaten egg white).
6. 6
   Gradually stir 3 tablespoons sour cream or yogurt into the remaining, thickened gelatin.
7. 7
   Spoon the gelatin on top of the previous layer (gently, so as to maintain a smooth surface).
8. 8
   Refrigerate again for about 15 minutes.
9. 9
   Repeat the above layering process for each of the remaining flavors. Be sure to cool adequately between layers to prevent melting and mixing.
10. 10
    Refrigerate for about 2 hours, until firm.
11. 11
    Remove the gelatin from the mold and place it (probably upside down) on a plate or smooth cutting board. Store refrigerated under saran wrap or aluminum foil. For best effect, serve sliced perpendicular to the layers, so each slice (approximately 1 cm thick) displays the full rainbow.