Preheat the oven to 350°F (180°C) and prepare an 8x8-inch baking pan lined with parchment paper.

In a medium bowl, combine vanilla wafer crumbs and ground hazelnuts if using. Add melted butter and mix until moistened, then press firmly into the bottom of the prepared pan.

Bake the crust for 10 minutes until set and golden, then let cool slightly.

Lower the oven temperature to 300°F (150°C).

In a large bowl, beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well after each. Blend in vanilla extract and warmed Nutella until just swirled.

Pour the cheesecake filling over the baked crust, spreading it evenly, and swirl the top to create marbled patterns.

Bake for approximately 40 minutes until the edges are set and the center is slightly jiggly.

Allow the bars to cool in the pan for 30 minutes, then refrigerate for at least 4 hours or overnight.

Once chilled, lift the bars out using the parchment and slice into squares before serving.