Cup of Yum
1. Preheat the oven to 375°F.

Make the crust:

Cup of Yum
1. In the bowl of a food processor pulse the crackers until finely ground. Pour in the butter and pulse until evenly moistened. Pour the crust into a 9-inch tart pan with a removeable bottom. Press the crust into the bottom and sides of the pan.
2. Bake for 7 minutes, or until fragrant. Allow to cool.

Make the caramel:

1. In a medium heavy bottomed saucepan, add the sugar and water. Turn heat to medium high and cook without stirring until the sugar dissolves and turns a medium amber color, about 10 minutes. Remove from heat.
2. Carefully whisk in the heavy cream, butter, and sour cream (the mixture will bubble up). Add in the salt and whisk until combined.
3. Pour into tart shell and allow to cool in the fridge while you make the Nutella filling.

Make the Nutella filling:

1. In a medium saucepan, whisk together the cornstarch and a few tablespoons of the heavy cream to form a smooth paste. Gradually whisk in the remaining cream. Add the Nutella and bring the mixture to a boil over medium heat. Whisking constantly, boil for 3 minutes or until the mixture has thickened.
2. Remove from heat and stir in the vanilla. Pour over the caramel in the tart shell.
3. Chill for 6 hours, or overnight, until the tart is set. The tart can be covered tightly and stored in the fridge for up to 3 days before serving.