Place water and lemon juice in 6-quart kettle (or pot). Add Sure Jell and stir well to dissolve.
Heat to boiling, add limoncello and return to a boil.
Add sugar all at once and bring back to a full, rolling boil (a boil that cannot be stirred down).
Add the butter and boil hard for exactly 1 minute.
Remove from heat, skim any foam.
Ladle hot jelly into jars leaving ¼-inch headspace.
Cover with lids and rings and process in boiling water bath or steam canner 5 minutes.
Remove jars and allow to cool undisturbed 24 hours on your countertop.
Jars are sealed when button on top of lid is fully depressed and won't flex up or down.
Store in pantry up to 1 year.
