In a small saucepan, combine cornstarch and water until smooth. Cook and stir over medium heat for 2-3 minutes or until thickened and opaque. Cool to room temperature.
In a large bowl, beat butter and vanilla until light and fluffy. Beat in cornstarch mixture. Gradually add confectioners' sugar; beat until frosting is light and fluffy.
Almond Frosting: Decrease vanilla extract to 1 teaspoon; add 1/2 teaspoon almond extract. Proceed as directed. Chocolate Frosting: Decrease confectioners’ sugar to 3-1/4 cups; add 1/4 cup baking cocoa. Sift ingredients together before adding to butter mixture. Proceed as directed.