# What You'll Need:
→ Rhubarb Layer
01 - Fresh rhubarb, trimmed and chopped - 14 oz
02 - Granulated sugar - 2.6 oz
03 - Fresh lemon juice - 1 tablespoon
04 - Cornstarch - 1 tablespoon
→ Shortbread Base and Crumble
05 - All-purpose flour - 1.76 cups
06 - Rolled oats - 1 cup
07 - Unsalted butter, cold and cubed - 10.6 tablespoons
08 - Light brown sugar - 3.5 oz
09 - Fine sea salt - 1/2 teaspoon
→ Custard Layer
10 - Whole milk - 1.27 cups
11 - Large egg yolks - 2
12 - Granulated sugar - 2.1 oz
13 - Cornstarch - 2 tablespoons
14 - Pure vanilla extract - 1 teaspoon
# How To Make:
01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, ensuring an overhang for easy removal of finished bars.
02 - In a saucepan, combine chopped rhubarb, granulated sugar, lemon juice, and cornstarch. Cook over medium heat while stirring frequently until rhubarb softens and the mixture thickens, approximately 8-10 minutes. Transfer to a bowl and allow to cool.
03 - In a large mixing bowl, combine flour, rolled oats, light brown sugar, and salt. Rub the cold cubed butter into the dry ingredients using your fingertips or a pastry cutter until the mixture resembles coarse breadcrumbs.
04 - Press two-thirds of the crumble mixture firmly and evenly into the prepared baking pan to create a compact base layer. Reserve the remaining crumble mixture for topping.
05 - Bake the base in the preheated oven for 15 minutes until it achieves a light golden color. Remove from oven and allow to cool slightly.
06 - Heat milk in a saucepan until steaming but not boiling. In a separate bowl, whisk together egg yolks, granulated sugar, and cornstarch until smooth. Slowly pour the hot milk into the egg mixture while whisking continuously. Return the combined mixture to the saucepan and cook over medium heat, stirring constantly, until thickened (2-3 minutes). Remove from heat and stir in vanilla extract.
07 - Spread the cooled rhubarb filling evenly across the baked base layer. Pour the prepared custard layer evenly over the rhubarb.
08 - Sprinkle the reserved crumble mixture evenly across the custard layer.
09 - Bake for 30 minutes, or until the crumble topping turns golden brown and the custard layer is set but still slightly soft.
10 - Allow the bars to cool completely within the baking pan. Refrigerate for a minimum of 2 hours before removing from the pan using the parchment paper overhang and cutting into 16 individual bars.
