WHISK first 5 ingredients in shallow dish until well blended; stir in piloncillo.
DIP bread slices, 1 at a time, in egg mixture, turning to evenly moisten both sides of each.
MELT butter in large nonstick skillet on medium heat. Add bread slices; cook 2 min. on each side or until golden brown on both sides. Top with cheese and raisins; cook 2 min. or until cheese is melted. Sprinkle with bacon.