In A Skillet, Saute Onion In Butter Until Tender. Remove From The Heat; Stir In Ham And Set Aside. Unroll Crescent Roll Dough Into One Long Rectangle. Press Onto The Bottom And 1 In. Up The Sides Of A Greased 13-In. X 9-In. X 2-In. Baking Dish; Seal Seams And Perforations. Spread With Reserved Ham Mixture. In A Bowl, Beat Eggs, Milk, Salt And Pepper; Stir In Cheese. Pour Over Ham. Sprinkle With Chives. Bake At 375 Degrees F For 23-28 Minutes Or Until A Knife Inserted In Center Comes Out Clean. Refrigerate Leftovers.