Make First Layer

1. In a medium saucepan, add water and 2 packets of powdered gelatin. Stir and let sit to bloom, 1 minute
2. Place over low heat, add sugar and stir. Allow to heat slightly and dissolve, about 5 minutes
3. Remove from heat and mix in lemon juice, limoncello, food coloring and lemon zest
4. Coat an 8" x 8" square baking pan with nonstick cooking spray. Pour in first layer, cover with plastic an refrigerate 30 minutes to 1 hour. You want the first layer to have some solidity (but, it doesn't have to be completely firm — you just don't want the two layers to mix)

Make Second Layer

1. In a medium saucepan, add water and 3 packets of powdered gelatin. Stir and let sit to bloom, 1-2 minutes
2. Place over low heat, add sugar and stir. Allow to heat slightly and dissolve, about 5 minutes
3. Remove from heat and add lemon juice and vodka
4. Carefully pour atop the first layer. Cover with plastic wrap and refrigerate 6 hours (but overnight refrigeration is recommended)

Invert & Slice

1. Run a knife along the outside of the gelatin. Place a plate atop the baking pan, and flip. Tap the pan's bottom a few times to release the gelatin. It should slide right out of the pan
2. Cut into squares (as large or as small as you'd like!) and garnish (if desired) upon serving. Refrigerate if not serving immediately