Arrange the peaches, cut side up, in an ovenproof dish and drizzle over the melted butter, then sprinkle over the sugar. Bake in a preheated oven, 230°C (450°F), Gas Mark 8, for 6–8 minutes until lightly brûléed.
Meanwhile, beat together the yogurt, crème fraîche, lemon rind and honey in a bowl until smooth and thick.
Arrange the peaches on 4 serving plates and top each with a dollop of the creamy yogurt mixture. Serve immediately, sprinkled with crushed amaretti biscuits.