My recipe uses
200 g golden syrup
115 g butter
115 g molasses (or black treacle)
115 g light brown sugar
200 g plain flour
2 tsp baking powder
2 tsp ground ginger
1 tsp bicarbonate of soda
100 g oats
1 egg
enough milk to make a dropping consistency.
Same method as yours and baking time is 60-75mins in an 8in square tin.
The only real difference between yours and mine is the wholemeal versus plain flour and twice the weight of oats in yours, oh and the shape of the tin. Mine doesn't sink
Silly question maybe, but you say it 'rose astronomically ' - you didn't add table spoons of bicarb instead of teaspoons did you? because I can't see why you got a huge rise with the listed ingredients