Heat oven to 350°F. Butter and flour two 8-inch round cake pans and set aside.
In a large mixing bowl, stir together sugar, flour, cocoa, baking powder, baking soda and salt. Add eggs, milk, oil and vanilla; beat on medium speed for 2 minutes. Stir in boiling water. Pour batter into prepared pans.
Bake 30 to 35 minutes or until top springs back when lightly touched in the center. Cool 10 minutes; remove from pans to wire racks. Cool completely.
In the bowl of your mixer, beat butter, melted chocolate, heavy cream and vanilla until smooth. Slowly add powdered sugar, scraping the sides of the bowl and beating on low until just combined., starting with 5 cups of powdered sugar and adding more if frosting is too thin.
Add crushed candy, increase mixer speed to high, and beat for one minute.
Assemble and frost cooled cake. Place uncovered in the refrigerator to chill for at least 2 hours.
In a microwave safe bowl, heat chocolate chips and heavy cream, stopping to stir every 20 seconds until smooth.
Let cool, then stir in honey or corn syrup.
Pour over the center of the cake, spreading gently to the edges and letting it drip down the sides.