30 min. before serving: Preheat oven to 350F.
In large bowl, with electric mixer at high speed,
beat egg whites until foamy; add cream of tartar,
beating until stiff, not dry. In small bowl, with
mixer at medium speed, beat yolks with 1/4 c. cold water
and salt until very light and fluffy;
carefully fold yolk mixture into beaten whites.

In a 10" ovenproof skillet, heat butter.
Add egg mixture; cook over low heat 3 min.
or until puffy and golden on underside
when lifted with a spatula. Then bake 10 min.
or until light brown and center springs back when pressed.

Run a spatula around sides to loosen omelet.
Make a cut through center of omelet, only partway thru,
perpendicular to handle.
Tip skillet at edge of warmed platter.
With spatula, fold omelet in half, then onto platter.
Spoon a filling into omelet. 2 servings.