Preheat your oven to 325°F (163°C). Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy lifting. Lightly grease if needed.

In a mixing bowl, combine graham cracker crumbs, melted butter, and sugar. Stir until the mixture resembles wet sand.

Press firmly into the bottom of the prepared pan in an even layer. Use the bottom of a glass or measuring cup to press it down.

Bake the crust for 10 minutes. Remove and let it cool slightly while you prepare the filling.

In a large bowl, beat the softened cream cheese until smooth and creamy. Add sugar and mix until well combined.

Add eggs one at a time, beating well after each. Mix in vanilla extract and sour cream. Continue mixing until the batter is smooth with no lumps.

Pour the cheesecake mixture over the cooled crust, smoothing it into an even layer with a spatula.

In a small microwave-safe bowl, combine Nutella and heavy cream. Heat in 20-second intervals, stirring between each, until the mixture is smooth and pourable.

Drop spoonfuls of the Nutella mixture over the cheesecake layer. Use a knife or toothpick to gently swirl it through the cheesecake, creating a marbled pattern.

Bake for 35–40 minutes, or until the center is set and the edges are slightly golden. Avoid overbaking; the center should jiggle slightly when moved.

Remove from oven and allow to cool completely to room temperature.

Refrigerate the cooled bars for at least 3 hours (or overnight) for best results.

Once chilled, use the parchment overhang to lift the cheesecake from the pan. Transfer to a cutting board and slice into bars.

Serve chilled and enjoy the creamy, chocolate-hazelnut perfection in every bite.