Step 1Heat the oven to 350 degrees. Butter and flour two 9-inch round cake pans. Line the bottoms with parchment paper, and butter the paper. Set aside.
Step 2Melt the Mexican chocolate and the unsweetened chocolate in a metal bowl over a pot of simmering water. Remove from the heat and set aside.
Step 3Sift the flour, baking powder, salt and cinnamon together. In the bowl of an electric mixer, beat the butter and sugar until well combined and creamy. Beat in the egg yolks and vanilla. On low speed, alternately add the flour mixture and milk, mixing just until all traces of flour are incorporated, ending with flour. Scrape down the sides of the bowl as needed. In a separate bowl, using clean beaters, beat the egg whites until stiff. Stir one-third of the egg whites into the cake batter. Gently fold in the remaining egg whites.
Step 4Divide the batter evenly between the cake pans, gently smoothing the top. Bake for 25 to 30 minutes, until a skewer inserted in the middle comes out clean. Cool the pans on a rack for 10 minutes. Run a knife around the inside edge of each pan to loosen the cakes. Remove the cakes from the pans and the parchment paper from the cakes. Cool completely before frosting.
Step 1Heat the cream in a small saucepan just until simmering.
Step 2Place the chopped Mexican chocolate and unsweetened chocolate in a bowl. Pour the hot cream over the chocolate. Let stand for a few minutes, then gently whisk until the chocolate has melted. Stir in the butter until melted, then add the corn syrup and Kahlua. Refrigerate for 20 to 30 minutes until stiff enough to spread. With a spatula, beat the ganache to make it smooth and spreadable.
Step 3Place one cake layer, bottom side up, on a serving platter. Frost the top with about one-third of the ganache, spreading it to the edges. Top with the second cake layer, again bottom side up. Spread the remaining ganache over the top and sides of the cake.