1) Preheat the oven to 190°C/gas mark 5. Butter the bottom of an 20cm baking dish and set aside.
2) Using a melon baller, clean out the red flesh from the centre of each peach. Arrange the peaches cut side up in the prepared dish. In the bowl of a food processor, add the amaretti cookies and pulse until finely crumbled. Divide the amaretti crumbs between the peaches. Fill the centre of each peach with the amaretti cookie crumbs. Sprinkle 1/2 tsp of sugar over each. Dot each peach with 1/2 tsp of butter.
3) Bake until the peaches are tender and the filling is crisp on top, about 30 mins. Serve warm with whipped cream.