Pre-heat the oven to 140C/275F/Gas 1.
Grease a 20cm/8in square cake tin with butter.
Sieve the flour, a pinch of salt, the ginger, nutmeg and mixed spice together into a large bowl.
Mix in the oatflakes.
Warm the tins of syrup and treacle in hot water to make it easier to measure them out accurately.
Put the syrup, treacle, butter and soft brown sugar into a small saucepan and melt over a gentle heat, bring up to a simmer but do not boil.
Stir into the flour mixture.
Mix in the beaten egg and milk to create a soft, almost pouring, consistency.
Pour into the buttered tin and bake for 1¼ hours, until firm in the centre.
Remove from the oven and leave in the tin for 5-10 minutes before turning out and cutting into squares.
For the hot spiced syrup, simply whisk all the ingredients together in a small pan and warm, but don't boil.
Place the rhubarb into a saucepan with a little water and the sugar.
Bring to a simmer and cook until just tender.
To serve, place a spoonful of rhubarb in the centre of the plate, top with a ball of ice cream.
Place a piece of parkin on the side and drizzle over the spiced syrup.