Preheat your oven to 425°F (220°C).
In a large saucepan, combine cherries, sugar, and cornstarch. Cook and stir over medium heat until the mixture thickens and bubbles. Stir in almond extract and lemon juice, then remove from heat.
Roll out half the pastry and line a 9-inch pie plate. Pour the cherry filling into the crust and dot with butter.
Roll out the remaining pastry and place over the filling. Trim, seal, and flute the edges. Cut slits in the top crust to allow steam to escape.
In a small bowl, whisk together the egg yolk and milk. Brush the mixture over the top crust.
Bake for 30 to 35 minutes, or until the crust is golden brown. If necessary, cover the edges with foil during baking to prevent over-browning.
Cool the pie on a wire rack before serving.