Heat the oven to 180C/fan 160C/gas 4. Sprinkle the sugar into the bottom of a baking tray, dot over the butter and add the spices. Put the peaches flat-side down on the mix and roast for 15-20 minutes, or until soft but still holding their shape.
Meanwhile, mix the vanilla with the mascarpone. Remove the peaches from the oven and while still warm, peel and discard the skin. Keep warm while you make the sauce.
Scrape the sugar from the tray into a small pan, and reduce the cooking liquor until you get a drizzling consistency.
Put 3 halves of peach per person on a plate, add a blob of the mascarpone, drizzle over the sauce and sprinkle over the amaretti biscuits.