For the espresso cake: Place a rack in the center of the oven and preheat the oven to 375 degrees F. Line two 8-inch round cake pans with parchment paper and grease with nonstick cooking spray.
In the bowl of an electric mixer, combine the cake mix, oil, vanilla liquor, espresso powder, vanilla extract, salt, eggs and 1 cup water. Beat on low speed for 30 seconds, and then on medium speed for 2 minutes, scraping the bowl with a spatula occasionally. Pour the batter evenly into the cake pans and smooth the tops with a spatula.
Bake until a toothpick inserted into the center of the cakes comes out clean, 28 to 30 minutes. Cool the cakes for 20 minutes in the pans, then turn the cakes out onto a wire rack to cool completely, about 1 hour.
For the caramel glass: Line a baking sheet with a silicone baking mat. Place the granulated sugar and vanilla liquor in a small saucepan and cook, without stirring, until the mixture is a deep amber color, about 5 minutes. Pour the caramel onto the prepared baking sheet and allow to cool to room temperature. Once cooled, break into shards.
For the Tuscan buttercream: Place the butter in the bowl of a stand mixer and beat with the paddle attachment until light and smooth, about 1 minute. Add the powdered sugar, vanilla liquor, vanilla extract and salt and beat on low until combined, about 30 seconds; increase the speed to medium and beat until fluffy, about 2 minutes.
Assembly: Place one of the cakes flat-side up on a cake stand, leveling the top of the cake with a serrated knife if necessary. Using a spatula, spread 1/4 cup of the buttercream evenly over the cake, leaving a 1/2-inch border. Place the other cake layer on top and frost the entire cake with the remaining buttercream, using the tip of the spatula to make decorative swirls in the buttercream. Press the chopped espresso beans around the outside of the cake and garnish the top with caramel glass.
Recipe courtesy of Giada De Laurentiis