Active Time
25 Mins
Total Time
1 Hour
Yield
Serves 16 (serving size: 1 bar)
Iain Bagwell

How to Make It

Step 1

Prepare the Cookie Base: Preheat oven to 350°F. Grease an 8-inch square baking pan with butter. Line pan with parchment paper, allowing paper to extend past edges of pan. Grease parchment. Pulse flour, powdered sugar, and salt in a food processor until combined, about 3 times. Add butter; pulse until mixture resembles coarse sand, 6 to 7 times. Press flour mixture into prepared pan. Bake in preheated oven 15 minutes.

Step 2

Prepare the Filling: Combine granulated sugar, lemon juice, cornstarch, and salt in a medium saucepan; bring to simmer over medium-high. (Do not bring to a boil.) Lightly beat eggs and yolks in a medium bowl. Add 1/2 cup of the hot sugar mixture to eggs, whisking constantly. Gradually add egg mixture to remaining sugar mixture in saucepan, whisking constantly. Cook, whisking constantly, until thick and bubbly, about 2 minutes. Remove from heat. Stir in butter until melted and combined. Spread hot filling evenly over prepared cookie base.

Step 3

Prepare the Topping: Pulse flour, powdered sugar, lemon zest, and salt in a food processor until combined, 5 to 6 times. Add butter; pulse until mixture forms pea-size pieces, 4 to 5 times. Add oats; pulse until combined, 2 to 3 times. Using your hands, press the mixture together into small clumps. Sprinkle clumps evenly over filling, pressing lightly to adhere. Bake at 350°F until top is lightly browned, 35 to 40 minutes.

Step 4

Cool completely in pan. Lift Lemon Crumble from pan using parchment as handles. Trim the edges, if necessary, and cut into 16 bars.