In the bowl of a food processor, measure out the cream cheese, sour cream, lemon zest, dill, horseradish, paprika, and crushed red pepper. *Add 1/2 cup sour cream if you want your dip thick and "spread-like" or 3/4 cup sour cream if you want it more loose like a dip.
Cover and puree the ingredients. Then scrape the bowl with a rubber spatula.
Now add the smoked salmon, green onions, and capers to the food processor. Cover and pulse until the salmon is broken into small pieces and well incorporated. You can puree it smooth, or leave it a little chunky.
Refrigerate at least one hour before serving.
DO NOT SALT. Both smoked salmon and capers are very salty. If you add salt or forget to rinse the capers, the dip might turn out too salty.