They should last up to 3 days. If stored in the freezer, they will last up to 7 days. Some sources say that they’re still good up to 2 months but I have not tried that yet. I only make these egg cups for a week’s supply.
Plenty. You can add small amounts of chopped onions, heavy cream (this will make fluffier egg cups), milk, tomatoes, broccoli, or paprika. Use whatever you like to make these egg cups more filling/exciting. Personally, I prefer keeping ingredients to a minimum as a strict ketoer and ketovore.