• Preheat oven to 350°F. Line an 8x8-inch baking dish with parchment paper, leaving overhang for easy removal. Lightly spray with nonstick cooking spray.

Shortbread Crust

• In a medium bowl, whisk flour, granulated sugar, and salt.
• Add the softened butter and mix with a fork or your hands until the mixture forms a moist, crumbly dough that holds together when squeezed (similar to damp sand with no dry patches).
• Press the dough firmly and evenly into the prepared pan. Use your hands or the bottom of a measuring cup to create a smooth, level surface.
• Bake for 15 to 18 minutes, or until the edges are lightly golden. While the crust bakes, prepare the filling.

Vanilla Cream Filling

• In a medium saucepan (not a heavy-bottom pan) over medium heat, whisk together the milk, heavy cream, sugar, cornstarch, and salt. Cook, whisking constantly, until thickened and gently bubbling, 4 to 6 minutes. Reduce heat to low.
• In a separate bowl, whisk together the eggs and vanilla. Slowly add about ½ cup of the hot milk mixture to the eggs to gently warm them (prevents curdling).
• Pour the egg mixture back into the saucepan. Continue cooking over low heat, stirring constantly, until thickened to a smooth, pudding-like consistency, about 2 to 3 minutes. Do not allow the mixture to boil.
• Immediately pour the hot filling over the pre-baked crust and spread into an even layer. Set aside.

Crumble Topping

• In a small bowl, whisk together the flour, brown sugar, and salt.
• Pour in the melted butter and stir with a fork until moist clumps form. Use your fingers to gently squeeze portions of the mixture to create a mix of small crumbs and larger clusters.
• Sprinkle the crumble evenly over the warm filling, lightly pressing a few larger pieces into the surface.
• Bake for 30 to 35 minutes, or until the topping is deep golden and the center has a slight jiggle (it will fully set as it cools).
• Let the bars cool completely in the pan on a wire rack, about 1 hour. Then refrigerate for at least 2 hours (or overnight) before lifting out with the parchment and cutting into bars.