Place a rack in middle of oven and preheat to 325°F. Pulse graham crackers in a food processor until very fine crumbs form (you should have about 2 cups). Add raw sugar, flour, and salt and pulse to combine. Add butter and pulse until mixture is the consistency of wet sand.
Transfer mixture to a 9" pie dish. Using a measuring cup, press firmly onto bottom and up sides of dish. Place pie dish on a rimmed baking sheet and bake crust, rotating halfway through, until dry and set, 20–25 minutes. Transfer pie dish to a wire rack and let crust cool.
DO AHEAD: Crust can be baked 1 day ahead. Store wrapped tightly at room temperature.
Toast walnuts on a rimmed baking sheet (oven should still be at 325°F), tossing occasionally, until slightly darker and fragrant, 8–10 minutes; let cool.
Pour white chocolate over cooled crust and, using a small offset spatula or the back of a spoon, spread over bottom and up sides, leaving 1/4" border along edge. Let stand until chocolate is set, 20–25 minutes.
Whisk eggs, corn syrup, brown sugar, barley malt syrup, malt powder, vinegar, salt, and vanilla in a medium bowl.
Melt butter in a small saucepan over medium heat. Cook, stirring often, until butter foams, then browns (do not let burn), about 5 minutes. Let cool slightly. Whisk brown butter into egg mixture, then fold in walnuts.
Place pie dish on a rimmed baking sheet and pour in filling. Bake, rotating halfway through, until set (center should not jiggle), 60–70 minutes. Transfer pie dish to a wire rack and let pie cool. Cover and chill at least 2 hours before slicing.
Serve pie topped with whipped cream, if desired.
DO AHEAD: Pie can be baked (without whipped cream) 2 days ahead. Keep chilled.
