Onion Tartlets, Caramelized

Cook onion, butter, water, salt, and pepper, covered, in a 10-inch heavy skillet over moderately low heat, 10 mi. Remove lid and cook, stirring frequently, until onion is deep golden brown and very tender, about 25 minutes. Fill tartlet shells and bake at 350 for 5-7 minutes. Top with a dollop of double cream or crème fraiche and chopped chives

Onion 2.5 c sweet, sliced very thin
Butter 2 T unsalted
Water 3 T
Tartlet 1 pkg, frozen, mini puff pastry
Crème Fraiche 0.25 c or double cream, room temp
Chives