Preheat oven to 350°. Microwave chocolate squares in a microwave-safe bowl at MEDIUM (50% power) 1 1/2 minutes or until melted, stirring at 30-second intervals. Stir until smooth.
Beat 1 cup butter and granulated sugar at medium speed with an electric mixer until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition. Add melted chocolate, beating just until blended.
Add flour, beating at low speed just until blended. Stir in vanilla and chocolate morsels. Spread batter into 2 greased and floured 9-inch tart pans with removable bottoms.
Bake at 350° for 20 minutes or until center is set. Cool in pans completely on wire racks (about 1 hour).
Beat 1/2 cup butter at medium speed with an electric mixer until creamy; gradually add powdered sugar alternately with milk, beating at low speed after each addition. Stir in peppermint oil.
Spread butter mixture over cooled tarts; cover and chill 1 hour or until firm.
Spread Chocolate Ganache over each tart. Sprinkle crushed peppermint candies around edges of tarts. Remove tarts from pans before serving, if desired.