Heat oven to 400.

Put a baking sheet on a rack and then put the peaches on the baking sheet, skin-side down.

In a food processor, puree almond paste, water, and lemon juice. Spoon mixture into the centers of the peaches.

Top each mound of almond paste with a piece of the butter.

Bake in the lower third of the oven until peaches are tender and almond paste is golden brown, about 25 minutes.

Serve warm.