Heat the oven: Preheat to 375°F (190°C). Lightly butter or oil a 9-inch square baking dish or similar 2-quart dish.

Prep the fruit: If using apples or pears, peel if you like and slice thin. For peaches or plums, slice. For berries or cherries, leave whole or halved as needed. Frozen fruit can go in straight from the bag—no thawing required.

Mix the fruit base in one bowl: Add fruit, 1–2 tablespoons lemon juice, 1–2 tablespoons cornstarch, and 2 tablespoons of the brown sugar. Toss until the fruit is evenly coated. Adjust sugar to taste if your fruit is very tart.

Set fruit in the baking dish: Pour the fruit mixture into the prepared dish and spread it evenly.

Make the crumble topping in the same bowl: To the now-empty bowl, add oats, flour, the remaining brown sugar, cinnamon, and salt. Stir to combine.

Add the fat: Drop in the cold cubed butter. Use your fingers to rub it into the dry mix until you have pea-sized clumps and sandy bits. If using coconut oil, break it into small pieces and mix similarly. Stir in nuts if using.

Top the fruit: Sprinkle the crumble evenly over the fruit. Don’t pack it down; loose crumbs crisp better.

Bake: Place the dish on a sheet pan to catch drips. Bake 35–45 minutes, until the topping is deep golden and the fruit is bubbling up around the edges.

Rest before serving: Let it cool for 15–20 minutes. This helps the juices set so each scoop holds together.

Serve: Enjoy warm with vanilla ice cream, whipped cream, or Greek yogurt. A drizzle of cream is great too.