Welcome to Spark! I hope you find every success here!!!
I'm sure one of the SparkPeople dieticians will have a better answer to your question, but here is what I do. First I figure it out on paper- list all the ingredients and write down their nutrition info for how much you used in the total recipe. Then add up the columns for calories, fat, protein, etc. Then figure out how many total portions there were, and divide by that number. Then when you go into the Nutrition Tracker, underneath the search button, there is "enter food not listed". I put it in there and save it as a favorite so I can go back and never have to do the math again.
Like I said, I'm sure there's probably an easier way...but that has worked well for me.
Glad you joined Spark and I hope you enjoy it as much as I do!