Step 1

Preheat oven to 350 degrees. Butter a 10-by-15-inch rimmed baking sheet. Line bottom with parchment paper, and butter parchment; set sheet aside.

Step 2

Make filling: Pulse raisins and sugar in a food processor until almost pureed. Transfer to a saucepan. Whisk cornstarch into 1 cup cold water; whisk into raisin mixture. Stir in cider. Simmer over medium-low heat, stirring occasionally, until mixture thickens and sugar has dissolved, about 6 minutes.Let cool completely.

Step 3

Make dough: Whisk together flour, baking soda, and salt in a medium bowl; set aside. Put shortening in the bowl of an electric mixer fitted with the paddle attachment. Mix on medium speed until smooth. Add brown sugar, and mix until pale and fluffy, 2 to 3 minutes. Add egg and vanilla, and mix until combined. Reduce speed to low. Add flour mixture; mix until just combined. Mix in oats.

Step 4

Press half the dough into prepared baking sheet. Spread raisin filling evenly over top of dough. Crumble remaining dough on top of filling using your fingers, gently pressing down so that topping covers filling. Bake, rotating sheet halfway through, until top is golden brown, about 35 minutes. Let cool completely in sheet on a wire rack. Cut into 2-inchsquares. Bars can be stored between layers of parchment in airtight containers at room temperature up to 5 days.