for the brownie base: Preheat oven to 325° F. To achieve ultra clean cuts, prepare a pan with a foil or parchment paper liner. Fold a long piece of heavy foil into a 13" wide strip and place inside a 9'' x 13'' metal baking pan, leaving overhang on 2 long sides. Spray foil lightly with nonstick spray. If you're not looking for perfect brownie cuts, simply spray pan with nonstick spray and eliminate the foil lining. Set pan aside.

In large heavy saucepan over low heat, stir together butter and chocolate until they are melted. Remove saucepan from heat and whisk in sugar, then eggs, one at a time. Whisk in vanilla and salt, and then sprinkle flour and espresso powder over the top. Stir to blend well.

Transfer batter to prepared pan. Bake brownies for 20 minutes and then remove from oven and let rest for 5 minutes.

for the Nutella cream cheese layer: While brownie base is baking, prepare the Nutella cream cheese layer. In the bowl of a stand mixer, cream together cream cheese and Nutella on medium-high speed until completely smooth and creamy, about 1 to 2 minutes. Add eggs, sugar, and sour cream, and beat on medium speed until just combined. Add vanilla and beat to combine.

Spread mixture evenly over warm brownie layer and tap the pan gently on the counter to settle it in. Return pan to the oven and bake for another 45 to 50 minutes, or until center no longer wobbles and edges are just a bit golden. Remove from oven and let cool completely before refrigerating. Chill for at least two hours before serving.

If you lined the pan with foil for clean cuts, use a knife to cut around the edges of the pan and loosen any areas that might have gotten stuck. Grab the 2 long foil edges and gently lift cheesecake from pan. Place on a large cutting board and cut into 2" squares. To achieve clean cuts, dip a long non-serrated knife into a tall glass of warm water after each cut, and then clean off the knife blade before cutting again.Top with sweetened whipped cream and chocolate shavings right before serving.