Pour 2 cups dry Champagne in medium-sized saucepan. Add 4 envelopes of Knox gelatin then let sit for 2 minutes so gelatin can activate.
Place over medium heat, whisking until gelatin dissolves. Whisk in ½ cup sugar until dissolved, then reduce heat to simmer.
In a separate bowl, pour 1 cup St. Germain elderflower liquor and 1 cup dry Champagne. Add 1–4 drops of pink or red food coloring then add to saucepan. Stir to completely incorporate ingredients then pour into a lightly greased 9" x 13" brownie pan.
Refrigerate overnight. Use lips-shaped cookie cutter to cut out jello shots then place on serving platter using a brownie spatula. Keep shots in refrigerator until ready to serve.
Notes
No St. Germain, no problem! Substitute amaretto liquor instead!