Whisk cream, ginger syrup, ground ginger, and honey until soft peaks form.
Stir in chopped stem ginger and freeze in a container for 2 hours until solid.
Preheat the oven to 140°C and butter a 30x20cm cake tin.
Melt brown sugar, butter, syrup, and treacle in a saucepan over low heat.
Mix oats, flour, spices, and salt in a bowl, then add eggs and milk.
Combine the melted sugar mixture with the dry ingredients and whisk well.
Pour into the tin and bake for 75 minutes until firm.
Cool the parkin in the tin before cutting into squares.
Reduce the oven temperature to 130°C.
Coat hazelnuts in beaten egg white and water, then toss with sugar and salt.
Bake nuts on a lined tray for 1 hour until golden-brown and cool.
Caramelize caster sugar in a frying pan and brush onto serving plates.
Serve parkin squares with hazelnuts, strawberries, lemon verbena, and ice cream.