Make the crumble topping

• Mix the flour, oats, brown sugar and salt in a bowl.
• Rub in the cold cubed butter with your fingertips until crumbly.

Assemble the crumble

• Spread the Nutella in an even layer in the baking dish.
• Scatter the crumble topping over the Nutella.

Bake

• Bake at 180 °C until the topping is golden and the Nutella is bubbling.

Cool and serve

• Let the crumble cool slightly before serving.