Preheat oven to 350 degrees F. Butter or lightly spray 2 large 12x18-inch baking sheets with sides with nonstick spray. Line bottom of pan with parchment paper then butter again or lightly spray with nonstick spray.
In a large mixing bowl beat egg yolks and 2 cups sugar with electric mixer on medium speed until well combined; beat in vanilla. In a small bowl whisk together flour cocoa powder, baking soda, and salt until mixed. Stir coffee into water until dissolved. Alternated adding flour mixture and coffee into eggs/sugar mixture while beating with electric mixer on low speed just until combined.
In a separate large mixing bowl beat egg whites with electric mixer on high speed until stiff peaks form. Fold into cake batter until just combined.
Spread batter into prepared pans. Bake at 350 degrees F for about 14-18 minutes or until toothpick inserted comes out clean. Cool slightly then run a knife along edges of pan to loosen cake. Turn cake over on work surface and remove parchment paper. Cool completely then using a 3-inch round biscuit or cookie cutter (or sharp knife) cut out cake into circles.
Prepare frosting by mixing together butter and powdered sugar in a large mixing bowl with electric mixer on medium speed. Beat in peppermint extract. Beat in powdered sugar 1 cup at a time until desired consistency.
Place a cake layer on work surface, top with frosting, then sprinkle with crushed candy canes, top with another cake layer and repeat with frosting, then candy canes, then top with a third cake layer. Repeat with remaining cake, frosting, and crushed candy canes. If there are any crushed candy canes left, sprinkle around sides of cakes.
Place heavy cream in a microwave safe bowl and microwave on high power in 30 second intervals until very hot and bubbly. Pour over chocolate chips in a bowl and stir together with corn syrup until smooth. (If mixture is not completely melted, microwave on half power in 15 second intervals, stirring after each interval, until smooth.) Cool slightly then spoon over tops of each cake. Store cakes in refrigerator until ready to serve. Cover cakes if storing for more than a few hours. Top with candy cane candy if desired before serving.
Makes about 14 cakes (your yield may vary slightly depending on how closely you cut your cake circles)
SNAPPY TIPS: The cake, frosting, and glaze can be made ahead of time and refrigerated then assemble cakes at a later time. Bring frosting to room temperature to soften before spreading on cakes and microwave glaze on half power in 15 second intervals until spreadable consistency. An alternative if you don’t want to make a homemade cake would be to follow the directions on a boxed cake mix for cupcakes, then cut the cupcakes in half horizontally, spread with frosting, then top with chocolate glaze (double the chocolate glaze recipe). If you have any leftover cake, frosting, and glaze make little “parfaits” in small glasses by layering cake and frosting then topping with glaze.SNAPPY SUBSTITUTIONS: If you don’t like dark chocolate, substitute regular unsweetened cocoa powder in the cake and bittersweet or semi-sweet chocolate chips for the chocolate glaze. You could also try other flavor combinations instead of peppermint. Substitute almonds and almond extract for the peppermint extract and candy canes, or any other flavor combination.