CRUST: Line a 9 x 13" cake pan with parchment paper. Melt milk chocolate in a double boiler. Stir peanut butter into melted chocolate. Place crushed corn flakes in a bowl and stir chocolate/peanut butter mixture over them, mixing well. Spread mixture evenly into prepared pan and cool in refrigerator. MOUSSE: Melt semisweet chocolate in a double boiler. Cream butter and sugar in a mixer fitted with a paddle, beating until light and fluffy. Add sifted cocoa powder and mix well. Scrape down bowl and add chocolate. Continue mixing and add egg yolks, one at a time, beating well after each addition. Fold in heavy cream that has been beaten to firm peak. Mix well to incorporate, leaving no white streaks in the chocolate. Spread mousse over crust. Chill about 2 hours, until set. Cut into desired size bars (1 x 4-1/2 " cuts) with a sharp knife dipped in hot water. Place bars on a cooling rack that has been placed over a clean baking sheet. If bars are soft, place rack in freezer until ganache is ready. (Bars may be completed at this time or coated with ganache) GANACHE: Melt chocolate in double boiler. Mix sugar and heavy cream in a small saucepan and bring mixture to a slow boil over low heat (be careful not to scorch the cream). Pour cream over chocolate and stir with a whisk to incorporate, making sure all the chocolate is melted. Strain mixture to remove any pieces of unmelted chocolate. Let cool for about 1 hour. Pour ganache over firm bars to coat. Refrigerate for 1 hour to firm ganache.