Heat oven to 350 degrees. Grease and flour a 9-inch springform pan, line it with parchment paper, and grease and sprinkle the parchment and sides with cocoa, tapping out the excess, and set aside.
In a saucepan over medium-low heat, melt the butter, then add chocolate. Melt, stirring frequently, until just smooth. Remove from heat, whisk in the vanilla extract, and let the mixture cool down so it won't curdle the eggs.
In a large bowl, whisk egg yolks with 1/3 cup sugar, then whisk in cooled chocolate mixture until well blended.
In another bowl with an electric mixer on medium speed, beat egg whites to soft peaks. Gradually add the remaining 2 tablespoons of sugar, and beat to stiff peaks.
Stir a little of the whites into the chocolate mixture to lighten it, then gently fold all the whites into chocolate. Scrape batter into prepared pan, and bake until cake springs back when gently touched in center, about 35 minutes. Transfer to a wire rack, and let cool for 20 minutes, then unclip sides, and transfer cake out onto rack, and cool completely. Store cake by wrapping well, and refrigerate for up to 5 days.
Make the sauce by melting the candy (be sure to reserve some for garnish), cream, and fluff in a small saucepan over medium heat until melted and smooth. Store in the refrigerator for up to a week. Gently heat when serving the cake. Drizzle sauce over each piece and garnish with some crushed candy.
Sauce is also great on ice cream and brownies.
