1/4 cup granulated sugar (adjust based on fruit sweetness)
1 tablespoon lemon juice
1 tablespoon cornstarch
1 cup all-purpose flour
1/2 cup rolled oats
1/2 cup packed brown sugar
1/2 cup cold unsalted butter, cubed
1/2 teaspoon ground cinnamon
1/4 teaspoon salt
2 cups whole milk
1/4 cup granulated sugar (for custard)
3 large egg yolks
1 teaspoon vanilla extract
Instructions
Preheat oven to 375°F (190°C). In a large bowl, combine fruit, 1/4 cup sugar, lemon juice, and cornstarch. Toss gently and transfer to a 9-inch square baking dish.
In another bowl, mix flour, oats, brown sugar, cinnamon, and salt. Cut in cold butter using a pastry blender or fingertips until mixture resembles coarse crumbs. Sprinkle evenly over fruit.
Bake for 35-40 minutes until fruit is bubbly and topping is golden brown. Let cool for 10 minutes.
Meanwhile, make custard: In a saucepan, heat milk over medium until steaming. In a bowl, whisk egg yolks and 1/4 cup sugar until pale. Slowly whisk hot milk into egg mixture, then return to saucepan.
Cook over medium-low heat, stirring constantly, until custard thickens enough to coat the back of a spoon (about 5-7 minutes). Do not boil. Remove from heat and stir in vanilla.
Strain custard through a fine-mesh sieve into a serving jug. Serve warm crumble with custard poured over.
Tips
For a gluten-free version, use gluten-free flour and oats.
Leftover crumble can be stored in the fridge for up to 3 days; reheat in oven or microwave.
Custard can be made ahead and reheated gently, adding a splash of milk if too thick.