1. Heat the oven to 400°. Put a rack on a baking sheet and then put the peaches on the rack, skin-side down.
2. In a food processor, puree the almond paste, water, and lemon juice. Spoon the almond mixture into the centers of the peaches. Top each mound of almond paste with a piece of the butter.
3. Bake in the lower third of the oven until the peaches are tender and the almond paste is golden brown, about 25 minutes. Serve warm.
Peeling the Peaches: Peel the peaches or not, as you like. The blush on the skin is pretty, but during taste tests most of us pulled off the peel and pushed it to the side of the plate.
Almond Paste: Almond paste is simply a combination of ground almonds and sugar. It's available in supermarkets, usually in the baking aisle, and comes in both cans and tubes.