1. Preheat your oven to 392°F or 200°C.

2. Line a baking pan measuring 8 inches by 12 inches (20x30 cm) with parchment paper.

3. Whisk together the eggs and sugar in a large bowl until the mixture becomes light and fluffy.

4. In a separate bowl, whisk the heavy cream and melted butter until smooth and fully incorporated.

5. Combine the dry ingredients in another bowl.

6. Add the cream mixture to the egg mixture and gently fold in the dry ingredients.

7. Evenly spread the mixture in the prepared baking pan and bake in the middle of the oven for about 25 minutes.

8. Melt the butter in a saucepan over medium heat, then add the hazelnuts, sugar, and heavy cream. Bring to a boil, reduce the heat and simmer for a few minutes, stirring occasionally.

9. Remove the cake from the oven and evenly spread the tosca sauce (or caramelized hazelnut sauce) over the top.

10. Return the cake to the oven and bake for an additional 5-10 minutes, or until the top is golden brown.

11. Let the cake cool completely before slicing it into bars.