1 14-oz can Sweetened Condensed Milk, well chilled 
1 (8-ounce) carton Key Lime Yogurt 
1 small banana, cut up 
1/3 cup key lime juice 
1 cup ice cubes 

In a blender, combine all ingredients except ice cubes and blend until smooth.  Add ice cubes gradually, with blender running, and continue blending until smooth.