Beat butter and brown sugar in a bowl with an electric mixer until light and creamy. Stir in flour and oats. Press into a greased 23x33cm slice pan. Bake for 15 minutes or until firm.
Beat eggs and caster sugar in a bowl with an electric mixer until light and fluffy. Beat in pumpkin and evaporated milk. Stir in salt and spices. Pour over pastry base.
Bake for 20 minutes or until filling is set. Cool; serve cut into squares.
To make pumpkin puree
Butternut pumpkin is the best type to use for making sweet things – like this slice and pumpkin pie. Peel the pumpkin and cut it into chunks, then steam and puree in a blender when cool. Steaming is better than boiling as you want as little liquid in the final puree as possible.