1. Prepare the cake: Place a rack in the middle of the oven and preheat to 375 degrees F. Butter two 8-inch (round) cake pans. Line the bottoms of each pan with a round of wax paper or parchment paper cut to fit the pans, and butter the paper.

2. Melt the 2 sticks of butter and the 8 ounces of chocolate together in a double boiler (or in a metal bowl set over a pan of barely simmering water), stirring constantly. (We like to use the work bowl of our stand mixer as the top bowl of the double boiler, so there are fewer dishes to do.) Remove the pan from the heat as soon as the mixture is smooth, transfer to the work bowl of a standing mixer, and stir in the vanilla and salt.

3. Pulse the 1 1/2 cups sugar and the mint together in a food processor until the mint is very finely chopped and pale green.

4. Add the mint sugar to the chocolate mixture and mix until smooth, about 1 minute on medium speed. With the machine on low, mix in the eggs one at a time, blending completely between additions. Sift the cocoa powder and flour over the batter and fold it in by hand until no dry spots remain. Divide the batter evenly between the two prepared pans and flatten the tops with a spatula.

5. Bake the cakes for 20 to 25 minutes, or until the tops of the cakes barely begin to crack. Let cool for about 5 minutes, then invert the cakes onto cooling racks and let cool completely.

6. Meanwhile, make the butter-cream: Bring a medium pot of water to a simmer over low heat. Place the 2 ounces chocolate and 1/2 teaspoon water in another small saucepan set over very low heat and cook until the chocolate is melted and the mixture is smooth. Cool.

7. Place the egg whites and 1/2 cup sugar in the bowl of a standing mixer and place over the simmering water and whisk for about 2 minutes or until dissolved. Remove the bowl from the pot and place in the mixer. Using the whisk attachment whisk the egg whites and sugar for about 3 minutes, or until the mixture has cooled down. Remove the whisk attachment and place the paddle attachment onto the mixer. Working on medium speed, add the 1 1/2 sticks butter one tablespoon at a time, whisking until smooth. Beat until the buttercream is smooth and thickened. Add the chocolate mixture and beat until smooth.

8. Spread 1 tablespoon of the frosting on the top of one cake, and place it top-side down on a cake platter. Spread a little less than half of the frosting onto this first cake, then place the second cake top-side up on the frosting. Use the remaining frosting to cover the rest of the cake. Sprinkle crushed candy canes around the perimeter of the cake, and chill until ready to serve, up to 24 hours ahead.

NOTE: To crush the candy, place in a tightly sealed plastic bag and pound with a rolling pin, or place in a food processor and whirl until finely ground.

VARIATION: If you are not a fan of fresh mint you can substitute 1 teaspoon vanilla or lemon extract in the cake batter.