Preheat oven to 180°C and butter a 2.5 litre shallow ovenproof dish.
Melt butter, sugar, treacle, and syrup in a saucepan over low heat until dissolved.
Simmer the mixture for one minute, then remove from heat and cool for five minutes.
Combine flour, bicarbonate of soda, spices, grated ginger, and chilli in a large bowl.
Whisk milk and beaten eggs into the warm treacle mixture.
Gradually stir the wet mixture into the dry ingredients to form a thick batter.
Pour batter into the dish and bake for 35-40 minutes until a skewer comes out clean.
Prepare toffee sauce by slicing remaining stem ginger into thin matchsticks.
Combine ginger strips, cream, sugar, and butter in a non-stick pan over low heat.
Stir until sugar dissolves, then simmer gently for 30 seconds.
Pour hot sauce over the baked sponge and serve with crème fraîche and lime zest.