To Make the Cake:

1. Preheat oven to 350°F. Place a parchment circle into the bottom of two 9-inch cake pans. Spray lightly with nonstick baking spray containing flour. Set aside.
2. Over a large bowl, sift together flour, sugar, cocoa powder, baking soda, baking powder and salt.
3. Add the eggs, buttermilk, espresso mixture, oil, and vanilla. Beat well to combine using a whisk or a mixer on low speed until no lumps remain. Batter will be thin.
4. Divide evenly between cake pans. Bake in preheated oven for 35-40 minutes, rotating pans in oven half way through. Remove pans to wire racks to cool for 20 minutes then invert, remove from pans and cool completely.

To Make the Frosting:

1. In a large bowl, sift together cocoa powder and espresso powder. Set aside.
2. In a small sauce pan over medium heat, bring 1 cup heavy cream to a boil. Pour hot cream over cocoa mixture and whisk until dissolved. Add remaining 1/2 cup cold heavy cream and granulated sugar. Whisk until sugar has dissolved. Cover and chill until cold, about 2 hours.
3. Remove cream from fridge. Add mascarpone and using a stand or hand mixer, beat on low speed until smooth. Increase speed and beat until thickened and medium peaks form, about 2-3 minutes. Do not over beat or the mixture will curdle.

To Assemble the Cake:

1. Place one cake layer cake plate or cake board. Top with 1 cup frosting and spread evenly over cake layer. Sprinkle with 1/2 cup toffee bits. Place second cake layer on top. Frost top with 1 cup frosting then frost sides of cake, reserving a bit of frosting to make 8 decorative swirls on top, if desired.
2. Sprinkle top of cake with remaining 1/2 cup toffee bits.
3. Using a small star tip, make 8 decorative swirls at even intervals around edge of cake. Place 1 large toffee piece into center of each swirl. Chill cake at least 2 hours before serving. Set at room temperature for 30 minutes prior to serving.