For the crust, position rack in the center of oven. Preheat oven to 350 degrees. Butter a 23 cm deep-dish pie pan or spring form pan.
In a medium mixing bowl, combine graham cracker crumbs and sugar. Add melted butter and stir until well combined. Press graham mixture evenly into bottom of pan and partially up sides. Bake 5 minutes to set crust. Remove from oven and let cook on rack.
For the fudge layer, sift flour, baking powder and salt into a medium mixing bowl. Set aside. In the top of a double boiler set over simmering water, combine butter and chocolate. Stir until melted and smooth. remove pan from heat and set aside to cool slightly.
In a large bowl of an electric mixer, combine sugar, egg and egg yolk and beat at medium-low speed until slightly thickened about 1 minute. Add vanilla and chocolate mixture and mix, beating on low speed, until well combined. Add dry ingredients and mix until just combined. Pour fudge layer on top of graham cracker crust. Bake 15-17 minutes or until fudge layer is almost set and a toothpick inserted in the center comes out with moist batter.
For the cream cheese layer, combine cream cheese and sugar and beat with electric mixer set at medium-low until smooth. Add egg and vanilla and beat until smooth. Gently spread mixture on top of fudge layer. Return pan to oven for 15 minutes. Remove pie from oven to cool slightly.
For the chocolate topping, combine milk chocolate and cream in the top of a double boiler set over simmering water. Stir until melted. With a spoon drizzle chocolate mixture on top of pie.
Place in refrigerator to set for 6 hours or overnight.