Beat egg whites in small bowl at high speed until foamy (1 to 2 minutes). Continue
beating, gradually adding 1/4 cup sugar, until glossy and stiff peaks form (2 to
3 minutes). Set aside.
Combine remaining 3/4 cup sugar and butter in large bowl. Beat at medium speed,
scraping bowl often, until creamy. Add egg yolks, lime juice and 1 tablespoon lime
peel. Continue beating until well mixed. Add flour and salt. Continue beating until
well mixed. Stir in milk by hand. Gently stir in beaten egg whites.
Pour mixture into ungreased 1 1/2-quart casserole. Place casserole dish into
a 13 x 9-inch baking pan. Place baking pan on oven rack; pour boiling water into
baking pan to 1/2-inch depth.
Bake for 42 to 52 minutes or until golden brown. Remove
from water; cool at least 30 minutes.
To serve, sprinkle with confectioners' sugar, if desired.
Garnish with whipped cream and grated lime peel, if desired.