Heat oven to 325 degrees. Spray bottom and sides of a 9 inch round pan with non stick spray. Line bottom of pan with parchment paper and then spray the parchment paper. Lightly flour sides of pan and the parchment paper.
For cake: put butter and unsweetened chocolate in double broiler or heat proof bowl and place over barely simmering water. Stirring frequently heat until smooth and melted. Remove from heat and cool slightly.
In a medium bowl, stir together flour, baking powder and salt. In another bowl, beat eggs, sugar and vanilla at medium speed until light and fluffy and well blended. On low speed, beat in melted mixture until combined. Beat in flour mixture just until incorporated. Gently stir in peppermint patties. Spoon batter into pan and smooth top with spatula. Bake 35-40 minutes until center springs back when lightly touched. Cool on wire rack for 15 minutes. Run knife around the edge and then invert onto wire rack. Remove the parchment paper. Cool completely. Turn cake right side up on serving platter.
Meanwhile, make glaze. Place chocolate in a large bowl. In a saucepan heat cream, butter and corn syrup, stirring occasionally, over medium heat until butter is melted and mixture is hot. Pour over the chocolate and let stand for 1 minute. Stir until chocolate is melted and glaze is smooth, then stir in vanilla.
Pour glaze over cake. Quickly, using the back of a spoon, spread over top and sides. Let stand 30 minutes. Sprinkle crushed candy over the top of the cake or make an edge around the cake with the candies.
If making the cake ahead of time, do not sprinkle the candies on until just before serving.
Store the cake ar room temperature. Can be made up to 1 day ahead of time.