Combine peaches and sugar in a saucepan; let stand 30 minutes or until mixture becomes syrupy. Cook over medium-low heat for 30 minutes.
Combine cornstarch and a small amount of water to form a smooth paste. Stir cornstarch mixture into peaches; bring to a boil. Reduce heat; cook, stirring constantly, until mixture becomes thickened and bubbly.
Remove from heat, and stir in butter and almond extract. Cool slightly. Spoon 2 teaspoons peach mixture into each tart shell.