Prepare the Panna Cotta:

1. Bloom the Gelatin: In a small bowl, sprinkle the gelatin over 2 tablespoons of cold water and let it sit for about 5 minutes to bloom.
2. Heat the Cream and Milk: In a saucepan, combine the heavy cream, milk, and sugar. Heat over medium heat, stirring occasionally until the sugar has dissolved and the mixture is warm but not boiling.
3. Add Hazelnut Paste/Spread: Once the cream and milk mixture is warm, stir in the hazelnut paste (or spread) until smooth and fully combined.
4. Dissolve the Gelatin: Once the hazelnut mixture is fully combined, remove the pan from the heat. Stir in the bloomed gelatin, making sure it dissolves completely into the mixture.
5. Add Vanilla: Stir in the vanilla extract for an extra depth of flavor.

Pour into Molds:

6. Pour into Molds: Divide the mixture evenly between 6-8 small serving cups or ramekins. Allow the panna cotta to cool slightly before placing it in the refrigerator to chill for at least 5 hours or overnight for best results.

Make the Chocolate Ganache:

7. Prepare the Ganache: In a small saucepan, heat the heavy cream until it begins to steam. Do not let it boil.
8. Melt the Chocolate: Remove from heat and pour the hot cream over the dark chocolate. Let it sit for a minute, then stir until the chocolate is completely melted and smooth. Add butter and vanilla extract, stirring until glossy.
9. Cool the Ganache: Let the ganache cool for about 10 minutes to thicken slightly.

Assemble the Dessert:

10. Top the Panna Cotta: Once the panna cotta has set, pour a generous spoonful of the chocolate ganache on top of each panna cotta. Spread it evenly with the back of a spoon.

Chill Again (Optional):

11. Chill for 10-15 Minutes: Let the assembled panna cotta with ganache chill for an additional 10-15 minutes in the fridge to set the ganache slightly.