# What You'll Need:
→ Rhubarb Layer
01 - 14 oz fresh rhubarb, trimmed and chopped
02 - 1/3 cup granulated sugar
03 - 1 tbsp lemon juice
04 - 1 tbsp cornstarch
→ Shortbread Base & Crumble
05 - 2 cups all-purpose flour
06 - 1 cup rolled oats
07 - 2/3 cup unsalted butter, cold and cubed
08 - 1/2 cup light brown sugar, packed
09 - 1/2 tsp salt
→ Custard Layer
10 - 1 1/4 cups whole milk
11 - 2 large egg yolks
12 - 1/4 cup granulated sugar
13 - 2 tbsp cornstarch
14 - 1 tsp vanilla extract
# How to Make It:
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 - Mix flour, oats, brown sugar, and salt in a large bowl. Work in cold butter using fingers or pastry cutter until mixture resembles coarse crumbs.
04 - Press two-thirds of crumble mixture firmly into pan bottom to create even base. Reserve remaining portion for topping. Bake base for 15 minutes until lightly golden, then remove from oven.
05 - Heat milk in saucepan until steaming but not boiling. Whisk egg yolks, sugar, and cornstarch until smooth. Gradually whisk in hot milk. Return mixture to pan and cook over medium heat, stirring constantly, until thickened, 2-3 minutes. Remove from heat and stir in vanilla.
06 - Spread cooled rhubarb evenly over par-baked base. Pour custard layer over rhubarb, spreading to cover completely.
07 - Sprinkle reserved crumble mixture evenly over custard layer. Bake for 30 minutes until crumble is golden brown and custard is set.
08 - Cool completely in pan. Refrigerate for at least 2 hours until firm. Lift from pan using parchment overhang and cut into 16 bars.
