Preheat an oven to 350*. Grease and line with parchment an 18" x 12" x 1/2'" cookie pan. Melt chocolate and butter over a double boiler or in the micro wave on short times stirring frequently. Mix flour and baking powder, set aside. In a mixer beat egg, sugar and vanilla on medium for 3 min. Stir in chocolate. Fold in flour. Pour onto pan and level out. Bake for about 20 min turning after 10 min. do not over bake. Brownie will be soft. Refrigerate until cold. When cold using a spatula remove the brownie from the pan, leaving the paper on. Cut the brownie in ½ widthwise. Then cut each piece in ½ again to make 12" x 4 ½" sections. Spread peanut butter on 3 pieces. Flip the one section with out peanut butter onto another section. Remove paper (the paper will help keep the brownie from cracking). Flip the other two on top. Chill until set. When chilled cut in 3 equal sections. Then each section in ½ and again in ½ so you have 6 sections. Cut each in ½ diagonally. Serve room temperature with chocolate sauce and vanilla ice cream.