Blend natvia in a high-speed blender until the consistency of icing sugar; reserve 2 teaspoons.
Process flour, powdered Natvia and butter until combined. Add egg yolk, water and vanilla; process until the ingredients just come together. Knead dough on a floured surface until smooth. Shape pastry into a disc; enclose in plastic wrap. Refrigerate for 30 minutes.
Roll pastry between sheets of baking paper until large enough to line a 25cm (10in) round loose-based tart tin. Ease pastry into tin; press into base and side, then trim edge. Place tin on an oven tray. Refrigerate for 20 minutes.
Preheat oven to 180C. Line pastry with a sheet of baking paper; fill with dried beans or rice. Bake for 15 minutes. Remove paper and beans; bake for a further 10 minutes or until pastry is golden brown. Cool.
Spread franfipane over tart base. Halve peaches; remove seeds. peel and cut each half into three wedges; arrange wedges on top of frangipane.
Bake tart for 45 minutes or until browned and set. Serve tart dusted with reserved sifted powdered Natvia.
*Frangipane: Process butter, almond meal, Natvia and flour until it forms a paste. Add eggs and vanilla; process until combined.