Prepare crust: In a food processor, add graham crackers, sugar and butter and pulse until blended. Press mixture evenly into a 9" square baking pan. Bake for approximately 8 minutes. Let cool on a wire rack.
Turn oven temp up to 400°F.
In a saucepan over medium heat, add holiday custard. Stir often to prevent scorching, until bubbles forms around the edges.
In a mixing bowl, beat eggs, sugar, salt, nutmeg and vanilla. Slowly blend in warmed custard.
Pour filling into baking pan and return to oven. Bake for approximately 30-35 minutes. Insert a knife in the center, if it comes out cleanly, remove from oven.
Cool completely on a wire rack.
Before serving top with hazelnut spread and sprinkle with white chocolate shavings and chopped hazelnuts.