Step 1

Heat oven to 350°F.

Step 2

Beat egg whites in bowl at high speed until foamy. Continue beating, gradually adding 1/4 cup sugar, until glossy, stiff peaks form. Set aside.

Step 3

Combine remaining 3/4 cup sugar and butter in another bowl. Beat at medium speed, scraping bowl often, until creamy. Add egg yolks, lemon juice and lemon zest; continue beating until well mixed. Add flour and salt. Beat at low speed until well mixed. Stir in milk. Gently stir in beaten egg whites.

Step 4

Pour mixture into ungreased 1 1/2-quart casserole dish. Place casserole into 13x9-inch baking pan. Place baking pan on oven rack; pour boiling water into baking pan to 1/2-inch depth. Bake 45-55 minutes or until golden brown. Remove casserole dish from water; cool 10 minutes. Sprinkle with powdered sugar, if desired.