Prep your dishes: Heat the oven to 375°F (190°C). Lightly butter 4–6 small ramekins (6–8 ounce size) or a muffin tin with large cups. Place them on a baking sheet lined with foil or parchment to catch drips.

Mix the fruit filling: In a bowl, toss the fruit with sugar, lemon juice, cornstarch, and any spices or vanilla. Taste a piece of fruit. If it’s very tart, add another spoon of sugar. The mixture should look lightly coated and glossy.

Make the crumble topping: In another bowl, mix flour, oats, brown sugar, and salt. Add the cold butter cubes. Use your fingertips or a pastry cutter to rub the butter into the dry mix until you get pea-sized clumps. Stir in nuts if using. The mix should clump when squeezed and crumble when you let go.

Fill the ramekins: Divide the fruit evenly among the dishes, packing gently so the fruit mounds slightly. Avoid overfilling to the brim to prevent boil-overs.

Add the topping: Sprinkle the crumble generously over each dish, covering the fruit fully with an even layer. Press lightly so it adheres but stays craggy on top for extra crunch.

Bake: Bake 20–28 minutes, until the topping is golden and the fruit is bubbling around the edges. Softer fruits like berries bake faster; apples and pears may need a few more minutes.

Rest and serve: Let the crumbles cool for 10–15 minutes. The juices will thicken as they rest. Serve warm with ice cream, whipped cream, or a dollop of yogurt.