1. Prepare the Crust:

1. Preheat oven to 225°F (110°C) and line a baking sheet with parchment paper.
2. In a small saucepan, melt butter over medium heat. Add brown sugar and hazelnuts, stirring until caramelized. Remove from heat and stir in vanilla. Let cool slightly.
3. In a clean bowl, beat egg whites and cream of tartar until soft peaks form. Gradually add granulated sugar, beating until stiff peaks form.
4. Gently fold the hazelnut praline mixture into the meringue, leaving streaks for a marbled effect.
5. Drop spoonfuls of the mixture onto the prepared baking sheet. Bake for 1.5 hours, then turn off the oven and let cool inside for another hour.