Preheat oven to 350 degrees F. Grease well a 9×13'' inch pan.
Chop the butter and the unsweetened chocolate into chunks and place together in a microwave safe bowl. Microwave in 30 second intervals, stirring in between, until melted. Set aside to cool, stirring occasionally.
In a large bowl beat the eggs, sugar, and vanilla until light and fluffy. While mixing, slowly add the melted chocolate. Add the peppermint extract.
In a separate small bowl combine the flour and baking powder. Stir the flour into the chocolate batter, just until combined. Pour batter into greased pan and bake for 20-30 minutes or until a knife poked in the center comes out clean.
Remove from oven and allow to cool completely.
Melt the chocolate and shortening together on very low heat in a double boiler, stirring constantly. Once melted, pour the melted white chocolate over the brownies and smooth into a thin layer. Sprinkle with crushed peppermint candies. Refrigerate until set. Cut into squares and then cut each square diagonally.