Stir well and bring to a low boil. Reduce the heat to low and simmer for 10 minutes, until the flavors have blended.
Adjust salt & pepper to taste.
Remove from heat and allow to cool.
Once cooled, transfer the sauce to a large bowl or container.
Take a hand blender and blend until smooth. The sauce may be blended in a standard blender as well, in small batches. Mix in the 3 tablespoons of sour cream until smooth.
Refrigerate until ready to assemble the enchiladas.