Peel the peaches with a vegetable peeler but leave whole.

Combine the granulated sugar, vanilla bean, lemon juice, and water in a saucepan. Bring to a simmer over moderate heat, stirring to dissolve the sugar. Add the peaches, cover, and adjust the heat to maintain a gentle simmer. Poach the peaches until they are barely tender, about 4 minutes; they will continue to cook as they cool. Remove them from the poaching liquid with a slotted spoon; reserve the syrup. When they are cool, halve the peaches and remove the pits.

Strain the syrup, let cool thoroughly, then pour it over the peach halves. Cover and chill the peaches.

Put the raspberries in a blender with 1/2 cup of the syrup from the chilled peaches. Blend until smooth, then strain through a fine-mesh sieve to remove the seeds. Thin the raspberry sauce if needed with a little more syrup. Taste and add a little superfine sugar if the sauce needs sweetening. To serve, cut each peach half into 3 slices. Make a pool of raspberry sauce on each of 6 dessert plates. Put a scoop of ice cream in the center. Surround with the peach slices. Crumble an amaretti cookie over the top and serve.