Preheat the oven to 140°C and grease a 20cm square cake tin with butter.
Sift the flour, salt, ginger, nutmeg, and mixed spice into a bowl and stir in the oats.
Melt the syrup, treacle, butter, and sugar in a saucepan over low heat until simmering.
Pour the melted mixture into the dry ingredients and stir to combine well.
Add the beaten egg and milk, stirring until the batter reaches a soft pouring consistency.
Pour the batter into the tin and bake for 50 minutes until the center is firm.
Cool the parkin in the tin for 10 minutes before turning it out and cutting into squares.
Combine sauce ingredients in a pan, boil, and simmer until thickened into a syrup.
Serve parkin squares topped with the warm syrup and a scoop of ice cream.