Slice onion and melt butter in pan on medium-high heat. Saute onion in pan until nicely carmelized. Remove from heat.
Place four tortillas on large non-stick cookie sheet. Slice dates and remove seed. Chop into 1/4 inch (or so) size pieces. Sprinkle onto the tortillas. Place carmelized onions on top of dates on tortillas. Put pieces of the blue cheese on the dates and onions. Finish off by putting additional tortilla on top of each.
Bake in oven heated to 350 for six minutes. Remove and cool for two minutes. Then slice into wedges and serve.