# 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 tbsp
04 - Cornstarch - 1 tbsp
→ Shortbread Base & Crumble
05 - All-purpose flour - 8.8 oz
06 - Rolled oats - 3.5 oz
07 - Unsalted butter, cold and cubed - 5.3 oz
08 - Light brown sugar - 3.5 oz
09 - Salt - 1/2 tsp
→ Custard Layer
10 - Whole milk - 10.1 fl oz
11 - Large egg yolks - 2
12 - Granulated sugar - 2.1 oz
13 - Cornstarch - 2 tbsp
14 - Vanilla extract - 1 tsp
# Step-by-Step:
01 - Preheat oven to 350°F. Line a 9-inch square baking pan with parchment paper, allowing overhang for easy removal.
02 - Combine rhubarb, sugar, lemon juice, and cornstarch in a saucepan. Cook over medium heat, stirring frequently, until rhubarb softens and mixture thickens, approximately 8-10 minutes. Set aside to cool.
03 - In a large bowl, combine flour, oats, brown sugar, and salt. Rub in cold butter with your fingertips or pastry cutter until mixture resembles coarse breadcrumbs.
04 - Press two-thirds of the crumble mixture firmly into the bottom of the prepared pan to form an even base. Reserve remaining crumble for topping.
05 - Bake the base for 15 minutes until lightly golden. Remove from oven and let cool slightly.
06 - Heat milk in a saucepan until steaming but not boiling. In a bowl, whisk egg yolks, sugar, and cornstarch until smooth. Gradually pour hot milk into egg mixture, whisking constantly. Return mixture to pan and cook over medium heat, stirring, until thickened, approximately 2-3 minutes. Remove from heat and stir in vanilla extract.
07 - Spread cooked rhubarb evenly over baked base. Pour custard layer evenly over rhubarb.
08 - Sprinkle reserved crumble mixture evenly over the custard layer.
09 - Bake for 30 minutes, or until crumble is golden and custard is just set.
10 - Cool completely in pan, then chill for at least 2 hours before lifting out and cutting into 16 bars.
