Preheat the oven to 200C/180C fan. Grease a 23cm pie dish and line with baking paper.
Cut 6 peaches in half. Remove stones. Split vanilla bean lengthways, then cut in half crossways. Place peach halves, vanilla beans pieces and butter in a large bowl with star anise and 2 tbsp of the Natvia. Toss well to combine.
Transfer to a roasting pan. Roast 20 mins until peaches are tender.
Meanwhile, easy pastry into pie dish and prick base all over with a fork. Cover and refrigerate 20 mins.
Remove peaches from roasting pan. Place cooking juices, vanilla, bean pieces and star anise in a small saucepan. Bring to boil. Simmer over low heat for 2 mins until reduced and syrupy.
Place pie dish on an oven tray. Line pastry with baking paper. Fill with dried beans or rice. Bake 20 mins. Remove paper and beans, then bake a further 5 mins until pale golden.
Meanwhile, process ricotta and remaining Natvia until well combined.
Spread ricotta mixture into pastry case. Place roasted peach halves on top. Bake tart 10 mins until pastry is golden and filling is heated through. Thinly slice remaining peaches. Serve tart topped with peach slices, drizzled with warm syrup.