Step 1: Preheat your oven to 350°F (175°C).
Step 2: Line a 9x13-inch baking pan with parchment paper.
Step 3: In a medium saucepan over low heat, combine the diced unsalted butter and chopped unsweetened chocolate. Stir until melted and smooth.
Step 4: In a large mixing bowl, whisk together the melted chocolate mixture and sugar until well combined. Add the eggs, one at a time, whisking well after each addition. Stir in the vanilla extract and kosher salt. Gradually fold in the flour and espresso powder until just combined.
Step 5: Pour the brownie batter into the prepared baking pan and spread it evenly. Bake for about 20-25 minutes, or until a toothpick comes out with a few moist crumbs.
Step 6: In a large mixing bowl, beat the softened cream cheese until smooth. Add in the Nutella and mix until combined. Gradually add the sugar, sour cream, and vanilla extract, mixing until fully incorporated. Finally, add the eggs one at a time.
Step 7: Once the brownie base has cooled slightly, use a mini muffin pan to scoop out small portions of the brownie batter, filling each cavity about halfway. Spoon the Nutella cheesecake filling on top.
Step 8: Return the mini muffin pan to the oven and bake for an additional 15-18 minutes, or until the cheesecake is set.
Step 9: Allow the bites to cool in the pan for a few minutes before transferring them to a wire rack to cool completely.
