When peaches are in season, this is the only dessert I make. Because nothing — nothing — beats a perfectly ripe peach that has been roasted until the sugars caramelize and it basically becomes candy. You halve the peaches, dot them with butter and a little brown sugar, roast until soft and golden, then top with a dollop of mascarpone sweetened with vanilla and a scattering of pistachios. It is summer in a bowl. Do not attempt this with unripe peaches. They need to be soft, fragrant, and at the