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° for 23-28 minutes or until a knife inserted in center comes out clean.