Preheat the oven to 180°C fan and line a 20cm square tin.
Mix the melted butter and brown sugar until smooth, then stir in the flour to make a soft, crumbly dough.
Press roughly two-thirds firmly into the base of the tin.
Toss the apples with the cinnamon and scatter evenly over the base.
Crumble the remaining dough over the top, leaving a few gaps for the apple to peek through.
Bake for 35–40 minutes until golden and the apples are soft.
Leave to cool completely in the tin before slicing - they’ll firm up as they cool.
