Preheat your oven to 350°F (175°C) and grease an 8x8-inch baking dish.

Combine chopped rhubarb, all-purpose flour, granulated sugar, baking powder, and beaten egg in a mixing bowl.

Pour the mixture into the prepared baking dish.

Mix brown sugar, flour, and salt in another bowl. Cut in cold butter until the mixture resembles pea-sized crumbs.

Sprinkle the crumble topping over the rhubarb filling in the baking dish.

Bake for 30-35 minutes until the top is golden brown and filling is bubbling.

Let cool slightly before serving warm with vanilla ice cream or whipped cream.