Prepare the crustPlace the biscuits/graham crackers into the bowl of a food processor. Blend until crumbs form. Add melted butter and process until completely combined.
Press the mixture with the back of the spoon and your fingers where necessary, into the bottom and edges of a rectangular 5×14 inch (12 x 36 cm) tart pan. Refrigerate for 30 minutes.
Prepare the fillingPlace the cream into a small saucepan and bring to a simmer. Remove from heat, add chocolate and Nutella and let sit 1 minute. Stir until smooth, chocolate completely melted and nutella is well combined.
Pour the chocolate mixture over the crust and spread evenly.
Refrigerate for 1-2 hours to set.
Prepare the meringuePlace the whites, sugar, cream of tartar and salt in a heat proof bowl. Place over a pan with simmering water (bain-marie).
Whisk constantly, for about 5 minutes, until it reaches 160F (71C).
Remove from heat and transfer to another bowl.
Start mixing on high speed for about 5-7 minutes, until glossy stiff peaks form. Incorporate vanilla extract while mixing.
Spread meringue over tart. Use a spoon to create some meringue picks. Toast the meringue with a brulee torch if desired.
Cut and serve. Keep the leftover tart refrigerated.