Boston Cream Pies

(makes 2). Heat oven to 350 degrees. Grease and flour 2 9-inch cake pans. For cake, in a large bowl, combine cake mix, egg yolks, water, and vanilla. Beat at medium speed for 4 minutes. Pour into pans. Bake for 28-31 minutes or until toothpick comes out clean. Cool completely. For filling, place sugar and cornstarch in a medium saucepan. Stir until blended. Add milk and beaten eggs. Cook on medium heat, stirring constantly, until thickened. Remove from heat. Stir in vanilla. Pour filling into a bowl. Press plastic wrap onto filling surface. Refrigerate for 3 hours or until completely chilled. To assemble, place each cake layer on a serving plate. Split layers in half horizontally. Spread half of the filling on the bottom layer of one cake. Place top layer on filling. Repeat for second cake. For glaze, combine frosting and butter in a bowl and microwave at 100% for 20-25 seconds or until smooth. Stir. Spread half of the glaze over the top of each cake. Refrigerate until ready to serve.