1-Step 1: Making the Oat Cookie Crust Preheat oven to 350°F. Cream softened butter, light brown sugar, and granulated sugar until fluffy and pale yellow. Add egg yolk at low speed; mix until sugar dissolves and mixture is pale white. Incorporate flour, oats, baking powder, baking soda, and salt at low speed until dough forms a slightly fluffy, fatty mixture. Spread dough about ¼ inch thick on a lined quarter sheet pan. Bake for 15 minutes; cool completely.

2-Step 2: Preparing the Pie Filling Mix dry filling ingredients on low speed until combined. Add melted butter; mix until dry ingredients are moistened. Add heavy cream and vanilla; mix thoroughly without aerating. Add egg yolks; mix just to combine without incorporating air. Use filling immediately.

3-Step 3: Assembling and Baking the Pie Pulse cooled oat cookie in a food processor with brown sugar and salt until crumbly like wet sand; if no processor, crumble by hand. Knead cookie crumbs with melted butter until mixture is moist enough to form a ball; add additional butter if needed. Press crust evenly into 9-inch pie plates, covering the bottom and sides. Store unbaked crust at room temperature for up to 5 days or refrigerated up to 2 weeks if not baking immediately. Preheat oven to 350°F. Divide filling evenly over crusts, filling about ¾ full. Bake for 15 minutes until golden brown on top but still jiggly. Open oven door and reduce temperature to 325°F; keep pies inside until oven cools (5-10 minutes), then close door and bake for 5 more minutes. If center is too jiggly, bake an additional 5 minutes. Cool pies at room temperature or refrigerate/freezer for quicker cooling. Optional: Freeze for 3 hours or overnight for denser filling. Dust with confectioners’ sugar before serving.