# What You'll Need:
→ Rhubarb Layer
01 - 14 oz fresh rhubarb, trimmed and chopped
02 - 5.3 oz granulated sugar
03 - 1 tablespoon fresh lemon juice
04 - 1 tablespoon cornstarch
→ Shortbread Base and Crumble
05 - 8.8 oz all-purpose flour
06 - 3.5 oz rolled oats
07 - 5.3 oz unsalted butter, cold and cubed
08 - 3.5 oz light brown sugar
09 - 1/2 teaspoon salt
→ Custard Layer
10 - 10 fl oz whole milk
11 - 2 large egg yolks
12 - 2.1 oz granulated sugar
13 - 2 tablespoons cornstarch
14 - 1 teaspoon vanilla extract
# Cooking Steps:
01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a saucepan, combine rhubarb, sugar, lemon juice, and cornstarch. Cook over medium heat, stirring often, until rhubarb softens and mixture thickens, approximately 8 to 10 minutes. Set aside to cool.
03 - In a large bowl, mix flour, oats, brown sugar, and salt. Rub in the cold butter with your fingers or a pastry cutter until the mixture resembles coarse crumbs.
04 - Press two-thirds of the crumble mixture firmly into the bottom of the prepared pan to form an even base. Reserve the remaining crumble for the topping.
05 - Bake the base for 15 minutes until lightly golden. Remove from oven and let cool slightly.
06 - In a saucepan, heat the milk until steaming but not boiling. In a bowl, whisk egg yolks, sugar, and cornstarch until smooth. Gradually pour in the hot milk, whisking constantly. Return mixture to the pan and cook over medium heat, stirring, until thickened, approximately 2 to 3 minutes. Remove from heat and stir in vanilla extract.
07 - Spread the cooked rhubarb evenly over the baked base. Pour the custard layer over the rhubarb.
08 - Sprinkle the reserved crumble mixture evenly over the top.
09 - Bake for 30 minutes, or until the crumble is golden and the custard is just set.
10 - Cool completely in the pan, then chill for at least 2 hours before lifting out and cutting into bars.
