In an extra-large mixing bowl, allow egg whites to stand at room temperature for 30 minutes. Meanwhile, sift the 1-1/2 cups powdered sugar and flour together 3 times; set aside.

Preheat oven to 350 degrees F. Add cream of tartar and the 1 teaspoon orange flower water or orange extract to egg whites. Beat with an electric mixer on medium speed until soft peaks form (tips curl). Gradually add granulated sugar, about 2 tablespoons at a time, beating until stiff peaks form (tips stand straight).

Sift about one-fourth of the flour mixture over beaten egg whites; fold in gently. Repeat, folding in remaining flour mixture by fourths, along with chopped edible flowers. Pour into an ungreased 10-inch tube pan. Gently cut through batter with a narrow metal spatula or knife to remove large air pockets.

Bake on the lowest rack of the oven for 40 to 45 minutes or until top of cake springs back when lightly touched. Immediately invert cake (leave in pan); cool thoroughly. Using a narrow metal spatula, loosen sides of cake from pan; remove cake.

In a large mixing bowl combine corn syrup and the 1/2 teaspoon orange flower water or orange extract. Stir in 2 cups of the sifted powdered sugar and orange juice. Stir in remaining 2 cups powdered sugar and enough of the hot water to make an icing of drizzling consistency.

To frost cake, lightly brush off any excess crumbs. Place cake on wire rack over a 15x10x1-inch baking pan. Use a spoon or ladle to pour icing over cake to cover the cake completely. Let stand 20 minutes. Repeat with a second layer of icing. Let dry 20 minutes. Repeat with a third layer of icing. If necessary, reuse the icing that has dripped on the pan, straining it to remove crumbs. Let icing dry completely. Place edible flowers in a circle around bottom edge of cake. If desired, place English daisies or other edible flowers in a tiny vase in center hole of cake. Makes 12 servings.

For a more colorful effect in the cake, use dried flower confetti. Spread 3 cups edible flower petals in a single layer on two 15x10x1-inch baking pans or cookie sheets. (Nasturtiums tend to darken and brown when dried, so you might want to avoid using them in the dried confetti.) Let stand 2 to 3 days until completely dry, stirring occasionally to help the drying process. Snip the dried flower petals into small pieces and measure 1/2 cup to use in the cake. Store remaining in an airtight container in a cool, dark place.

Up to 1 month ahead, make, bake, and cool cake as directed. Do not frost. Place cooled cake in a large freezer bag and freeze. Before serving, thaw at room temperature for several hours. Frost as directed.