Mix sour cream with cream cheese, until well blended. Add onions, ham, chilies and cheddar, mixing gently.
Slice the top off of the bread round and carefully cut the middle out of the bread to form a bowl. Cube the removed bread for serving. Spoon the cheese mixture into the bowl, replace the top to form a lid.
Bake at 350 degrees F for 30 minutes. Serve warm, with toasted bread cubes, crackers, or tortilla chips.