Kristen Aiken, an online editor for marthastewart.com, joins Martha to make her great-grandmother's recipe for raisin pie.
On a lightly floured work surface, roll 1 piece of pie crust into a 12-inch round. With a dry pastry brush, sweep off the excess flour; fit dough into a 9-inch pie plate, pressing it into the edges. Cover with plastic wrap; chill pie shell until firm, about 30 minutes.
In a medium saucepan, mix together raisins, water, cornstarch, sugar, vinegar, salt, cinnamon, and butter. Bring to a gentle boil over medium-high heat. Let boil until very thick, stirring constantly, 2 to 3 minutes. Remove from heat and let cool slightly.
Preheat oven to 450 degrees. Pour raisin mixture into pie shell. On a lightly floured work surface, roll remaining piece of pie crust into a 12-inch round. Using a 1 1/4-inch heart-shaped cookie cutter, cut out 8 decorative heart shapes in a circular pattern, from center of the top crust. Lay over raisin mixture. Trim top and bottom edges, leaving a 1-inch overhang; press lightly to seal, then fold under and press again. Crimp edges as desired.
In a small bowl, whisk together egg yolk, milk, and salt. Brush egg mixture over crust and place pie on a rimmed baking sheet. Transfer to oven and bake until crust is golden and filling is bubbly, 25 to 30 minutes. Serve with vanilla ice cream.