Heat oven to 160C/140C fan/gas 3. Butter a deep 22cm square cake tin and line with baking parchment.
Beat the egg and milk together with a fork.
Gently melt the syrup, treacle, sugar and butter in a large saucepan until the sugar has dissolved. Remove from the heat.
Mix together the oatmeal, flour and ginger and stir into the syrup mixture making sure there are no bits of flour showing. Add the egg and milk mixture.
Pour the mixture into the prepared tin and bake for 50 mins to 1 hr until the cake feels firm and a little crusty on top. Cool in the tin before cutting into 16 squares.
Wrap the cake in more parchment and tin foil.
Keep for five days before eating if you can as it becomes softer and stickier the longer you leave it, up to two weeks. Lisa Seeley