Pre-cook the fruit

• Halve and stone the plums and dice the apple.
• Place the fruit in a baking dish with the sugar and toss to coat.
• Bake at 180 °C so the plums soften and shrink, leaving room for the topping.

Make the crumble topping

• Rub the cold butter into the flour with your fingertips.
• Add the sugar, a pinch of salt and the chopped mixed nuts.
• Mix until you get a coarse, crumbly texture.

Assemble and bake

• Press the cooked fruit down lightly in the dish.
• Scatter the crumble generously over the top.
• Bake until golden and bubbling.

Serve

• Serve warm with a scoop of vanilla ice cream.