• Grease and line base and sides of a 9 x 13-inch (23 x 33cm) baking pan with parchment paper.
• Combine flour, sugar, butter and salt together in a large bowl; mix until well combined and the mixture holds together when you clench some of it in your fist. Press half of the mixture over the of the base of the pan using a flat bottom glass, then an off-set spatula or something similar, to flatten around the edges of the pan. Place in the fridge for 10 minutes.
• Preheat the oven to 350°F (180°C).
• Cook the base for 20 to 25 minutes or until a light golden brown. Set aside.

To make the filling:

• Melt the butter in a large frying pan over medium-high heat. Add the apple, sugar, cranberries, nutmeg and salt. Cook, covered, stirring occasionally, for 5 minutes. Remove the lid and cook for about 3 minutes, stirring occasionally, until any liquid has been absorbed or evaporated and apples are softened but not mushy.
• Spoon the filling over the base, spreading in an even layer. Sprinkle the remaining crumble (base) mixture over the apple mixture. Bake for 40 minutes or until golden brown. Let stand in the pan to cool completely before dusting it with powdered sugar and cutting into 16 equal-sized bars.